Multichannel optical coupler

ABSTRACT

The optical fiber coupler array can be capable of providing a low-loss, high-coupling coefficient interface with high accuracy and easy alignment between a plurality of optical fibers (or other optical devices) with a first channel-to-channel spacing, and an optical device having a plurality of closely-spaced waveguide interfaces with a second channel-to-channel spacing, where each end of the optical fiber coupler array can be configurable to have different channel-to-channel spacing, each matched to a corresponding one of the first and second channel-to-channel spacing. Advantageously, the refractive indices and sizes of both inner and outer core, and/or other characteristics of vanishing core waveguides in the optical coupler array can be configured to reduce the back reflection for light propagating from the plurality of the optical fibers at the coupler first end to the optical device at the coupler second end, and/or vice versa.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/923,383, entitled “MULTICHANNEL OPTICAL COUPLER ARRAY,” filed Oct.18, 2019, and is a continuation-in-part of U.S. application Ser. No.16/141,314, entitled “MULTICHANNEL OPTICAL COUPLER,” filed Sep. 25,2018, which is a continuation-in-part of U.S. application Ser. No.15/811,462, entitled “MULTICHANNEL OPTICAL COUPLER ARRAY,” filed Nov.13, 2017, which is a continuation-in-part of U.S. application Ser. No.15/459,730, entitled “MULTICHANNEL OPTICAL COUPLER ARRAY,” filed Mar.15, 2017, which claims the benefit of U.S. Provisional Application No.62/417,180, entitled “MULTICHANNEL OPTICAL COUPLER ARRAY,” filed Nov. 3,2016 and which is a continuation-in-part of U.S. application Ser. No.14/306,217, entitled “OPTICAL COMPONENT ASSEMBLY FOR USE WITH AN OPTICALDEVICE,” filed Jun. 16, 2014, which claims the benefit of U.S.Provisional Application No. 61/834,957, entitled “OPTICAL COMPONENTASSEMBLY FOR USE WITH AN OPTICAL DEVICE,” filed Jun. 14, 2013. U.S.application Ser. No. 15/811,462 also claims the benefit of U.S.Provisional Application No. 62/564,178, entitled “MULTICHANNEL OPTICALCOUPLER ARRAY,” filed Sep. 27, 2017 and is a continuation-in-part ofU.S. application Ser. No. 15/617,684, entitled “CONFIGURABLEPOLARIZATION MODE COUPLER,” filed Jun. 8, 2017, which is acontinuation-in-part of U.S. application Ser. No. 15/459,730, entitled“MULTICHANNEL OPTICAL COUPLER ARRAY,” filed Mar. 15, 2017, which claimsthe benefit of U.S. Provisional Application No. 62/417,180, entitled“MULTICHANNEL OPTICAL COUPLER ARRAY,” filed Nov. 3, 2016 and which is acontinuation-in-part of U.S. application Ser. No. 14/306,217, entitled“OPTICAL COMPONENT ASSEMBLY FOR USE WITH AN OPTICAL DEVICE,” filed Jun.16, 2014, which claims the benefit of U.S. Provisional Application No.61/834,957, entitled “OPTICAL COMPONENT ASSEMBLY FOR USE WITH AN OPTICALDEVICE,” filed Jun. 14, 2013. This application is also acontinuation-in-part of U.S. application Ser. No. 14/677,810, entitled“OPTIMIZED CONFIGURABLE PITCH REDUCING OPTICAL FIBER COUPLER ARRAY,”filed Apr. 2, 2015, which claims the benefit of U.S. ProvisionalApplication No. 61/974,330, entitled “OPTIMIZED CONFIGURABLE OPTICALFIBER COUPLER ARRAY,” filed Apr. 2, 2014. The entirety of eachapplication referenced in this paragraph is expressly incorporatedherein by reference.

BACKGROUND Field of the Invention

The present disclosure relates generally to an optical coupler array,e.g., a multichannel optical coupler array, for coupling, e.g., aplurality of optical fibers to at least one optical device. Someembodiments can relate to coupling light to and from a plurality offibers, such as to and from one or more single mode fibers, few-modefibers, multimode fibers, multicore single mode fibers, multicorefew-mode fibers, and/or multicore multimode fibers. Some embodiments canrelate to coupling light to and from photonic integrated circuits (PICs)and to and from multicore fibers (MCFs). Some embodiments can includefiber arrays used in coherent or incoherent beam combining applications.Some embodiments can relate generally to high power single mode lasersources, and to devices for coherent combining of multiple optical fiberlasers to produce multi-kilowatt single mode laser sources. Someembodiments may relate to phase locked optical fiber components of amonolithic design that may be fabricated with a very high degree ofcontrol over precise positioning (e.g. transverse or cross-sectionalpositioning) of even large quantities of plural waveguides, and that maypotentially be configurable for increasing or optimization of thecomponents' fill factor (which can be related to the ratio of the modefield diameter of each waveguide at the “output” end thereof, to thedistance between neighboring waveguides).

The present disclosure also relates generally to couplers for providingoptical coupling between a plurality of optical fibers (or other opticaldevices) and an optical device having a plurality of waveguideinterfaces, and more particularly to a configurable optical fibercoupler device comprising an array of multiple optical fiber waveguides,configured to provide, at each of its ends, a set of high opticalcoupling coefficient interfaces with configurable numerical apertures(which may be the same, or may vary between coupler ends), where thechannel-to-channel spacing at the coupler second end is smaller than thechannel-to-channel spacing at the coupler first end, thus enablingadvantageous coupling between a number of optical devices (includingoptical fibers) at the coupler first end, and at least one opticalwaveguide device with at least a corresponding number of closely-spacedwaveguide interfaces at the coupler second end.

Description of the Related Art

Optical waveguide devices are useful in various high technologyindustrial applications, and especially in telecommunications. In recentyears, these devices, including planar waveguides, two or threedimensional photonic crystals, multi-mode fibers, multicore single-modefibers, multicore few-mode fibers, and multicore multi-mode fibers arebeing employed increasingly in conjunction with conventional opticalfibers. In particular, optical waveguide devices based on refractiveindex contrast or numerical aperture (NA) waveguides that are differentfrom that of conventional optical fibers and multichannel devices areadvantageous and desirable in applications in which conventional opticalfibers are also utilized. However, there are significant challenges ininterfacing dissimilar NA waveguide devices and multichannel deviceswith channel spacing less than a diameter of conventional fibers, withconventional optical fibers. For example, in some cases, at least someof the following obstacles may be encountered: (1) the differencebetween the sizes of the optical waveguide device and the conventionalfiber (especially with respect to the differences in core sizes), (2)the difference between the NAs of the optical waveguide device and theconventional fiber, and (3) the channel spacing smaller than thediameter of conventional fibers. Failure to properly address theseobstacles can result in increased insertion losses and a decreasedcoupling coefficient at each interface.

For example, conventional optical fiber based optical couplers, such asshown in FIG. 6 (Prior Art) can be configured by inserting standardoptical fibers (used as input fibers) into a capillary tube comprised ofa material with a refractive index lower than the cladding of the inputfibers. However, there are a number of disadvantages to this approach.For example, a fiber cladding-capillary tube interface becomes a lightguiding interface of a lower quality than interfaces inside standardoptical fibers and, therefore, can be expected to introduce opticalloss. Furthermore, the capillary tube must be fabricated using a costlyfluorine-doped material, greatly increasing the expense of the coupler.

U.S. Pat. No. 7,308,173, entitled “OPTICAL FIBER COUPLER WITH LOW LOSSAND HIGH COUPLING COEFFICIENT AND METHOD OF FABRICATION THEREOF”, whichis hereby incorporated herein in its entirety, advantageously addressedsome of the issues discussed above by providing various embodiments ofan optical fiber coupler capable of providing a low-loss, high-couplingcoefficient interface between conventional optical fibers and opticalwaveguide devices.

Nevertheless, a number of challenges still remained. With theproliferation of multichannel optical devices (e.g., waveguide arrays),establishing low-loss high-accuracy connections to arrays of low or highNA waveguides often was problematic, especially because the spacingbetween the waveguides is very small making coupling thereto all themore difficult. U.S. Pat. No. 8,326,099, entitled “OPTICAL FIBER COUPLERARRAY”, issued Dec. 4, 2012, which is hereby incorporated herein byreference in its entirety, endeavors to address the above challenge byproviding, in at least a portion of the embodiments thereof, an opticalfiber coupler array that provides a high-coupling coefficient interfacewith high accuracy and easy alignment between an optical waveguidedevice having a plurality of closely spaced waveguides, and a pluralityof optical fibers separated by at least a fiber diameter.

U.S. Pat. No. 8,712,199, entitled “CONFIGURABLE PITCH REDUCING OPTICALFIBER ARRAY”, which is expressly incorporated by reference herein,discusses the importance of cross sectional or transverse positioningaccuracy (precise cross sectional positioning in some cases) of theindividual waveguides. Improved cross sectional positioning accuracy ofthe waveguides remains desirable.

It is also desirable to improve and/or optimize optical coupling betweena set of isolated fibers (e.g., single mode fibers) at one end andindividual modes (e.g., of a few-mode or multimode fiber) and/or cores(e.g., of a multicore fiber) at another end. Further fiber arrayimprovements can be desirable.

Furthermore, for many practical applications of a coupler array, theback reflection (or return loss) of light traveling therethrough, at oneof, or at both first and second end(s) of the coupler array can be veryimportant. For example, improvement (e.g., optimization) to reduce backreflection can be critical for some telecommunication and for somesensing applications (e.g., when light inserted into the coupler arrayis used for sensing), because back reflections can undesirably distortthe characteristics of light being sensed and thus can negatively impactsensor performance. Accordingly, it can be advantageous in variousimplementations, if the refractive indices and sizes of both inner andouter core, and/or other characteristics of vanishing core waveguides inthe optical coupler array could be improved (e.g., optimized) to reducethe back reflection for light propagating from the plurality of theoptical fibers at the coupler first end to the optical device at thecoupler second end, and/or vice versa

SUMMARY

Example embodiments described herein have innovative features, no singleone of which is indispensable or solely responsible for their desirableattributes. Without limiting the scope of the claims, some of theadvantageous features will now be summarized.

Example Set I

1. A multichannel optical coupler array for optical coupling of aplurality of optical fibers to an optical device, comprising:

-   -   an elongated optical element having a first end operable to        optically couple with said plurality of optical fibers and a        second end operable to optically couple with said optical        device, and comprising:        -   a common single coupler housing structure;        -   a plurality of longitudinal waveguides each positioned at a            spacing from one another, each having a capacity for at            least one optical mode, each embedded in said common single            housing structure proximally to said second end, wherein at            least one of said plurality of longitudinal waveguides is a            vanishing core waveguide configured to be coupled at said            first end to one of said plurality of optical fibers having            a propagating mode with an effective refractive index            NeffFiber and configured to be coupled at said second end to            said optical device having a mode with an effective            refractive index NeffDevice, said at least one vanishing            core waveguide having an effective refractive index Neff1            for said at least one optical mode at said first end and            Neff2 at said second end, each said at least one vanishing            core waveguide comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having a first inner core size (ICS-1) at                said first end, and a second inner core size (ICS-2) at                said second end; and            -   an outer core, longitudinally surrounding said inner                core, having a second refractive index (N-2), and having                a first outer core size (OCS-1) at said first end, and a                second outer core size (OCS-2) at said second end; and        -   an outer cladding, longitudinally surrounding said outer            core, having a third refractive index (N-3), a first            cladding size at said first end, and a second cladding size            at said second end,    -   wherein said common single coupler housing structure comprises a        transversely contiguous medium having a fourth refractive index        (N-4) surrounding said plurality of longitudinal waveguides,        wherein a relative magnitude relationship between said first,        second, and third refractive indices (N-1, N-2, and N-3,        respectively), comprises the following magnitude relationship:        (N-1>N-2 >N-3), wherein a total volume of said medium of said        common single coupler housing structure, is greater than a total        volume of all said vanishing core waveguides inner cores and        said outer cores confined within said common single coupler        housing structure, wherein said first inner vanishing core size        (ICS-1), said first outer core size (OCS-1), and said spacing        between said plurality of longitudinal waveguides, are        simultaneously and gradually reduced, in accordance with a        reduction profile, between said first end and said second end        along said elongated optical element, until said second inner        vanishing core size (ICS-2) and said second outer core size        (OCS-2) are reached, wherein said second inner vanishing core        size (ICS-2) is selected to be insufficient to guide light        therethrough, and said second outer core size (OCS-2) is        selected to be sufficient to guide at least one optical mode,        such that:        -   light traveling in a first direction from said first end to            said second end escapes from said inner vanishing core into            said corresponding outer core proximally to said second end,            and        -   light traveling in a second direction from said second end            to said first end moves from said outer core into said            corresponding inner vanishing core proximally to said first            end,    -   wherein said common single coupler housing structure proximally        to said first end has a cross sectional configuration comprising        a transversely contiguous structure with at least one hole,        wherein the at least one hole contains at least one of said        plurality of longitudinal waveguides creating a gap between the        coupler housing structure and the at least one of said plurality        of longitudinal waveguides, and    -   wherein the relationship between said Neff1, Neff2, NeffFiber,        and NeffDevice is one of:        -   (1) Neff2 is substantially equal to NeffDevice and Neff1 is            not equal to NeffFiber;        -   (2) Neff1 is substantially equal to NeffFiber and Neff2 is            not equal to NeffDevice; or        -   (3) Neff1 is larger than NeffFiber and Neff2 is smaller than            NeffDevice.

2. The multichannel optical coupler array of Example 1, wherein in atleast one of said vanishing core waveguides comprises a refractive indexprofile in which:

-   -   said first refractive index (N-1),    -   said first inner core size (ICS-1),    -   said second inner core size (ICS-2),    -   said second refractive index (N-2),    -   said first outer core size (OCS-1),    -   said second outer core size (OCS-2), and    -   said third refractive index (N-3),    -   are configured to reduce at an optical fiber interface and/or at        an optical device interface, back reflection of the light        traveling in at least one of: in said first direction from said        plurality of optical fibers to said optical device, or in said        second direction from said optical device to said plurality of        optical fibers.

3. The multichannel optical coupler array of Example 1, wherein saidNeff1 is larger than NeffFiber and said Neff2 is substantially equal toNeffDevice.

4. The multichannel optical coupler array of Example 3, wherein said oneof said plurality of optical fibers has a core refractive indexNcoreFiber and cladding refractive index NcladdingFiber and said opticaldevice has a mode with core refractive index NcoreDevice and claddingrefractive index NcladdingDevice, and wherein said N-3 is substantiallyequal to NcladdingFiber, N-2 is substantially equal NcoreDevice, and N-1is substantially equal to (N-2)+(NcoreFiber-NcladdingFiber).

5. The multichannel optical coupler array of Example 1, wherein saidNeff1 is substantially equal to NeffFiber and said Neff2 is smaller thanNeffDevice.

6. The multichannel optical coupler array of Example 5, wherein said oneof said plurality of optical fibers has a cladding refractive indexNcladdingFiber, and wherein said third refractive index (N-3) in atleast one of said vanishing core waveguides is lower than saidNcladdingFiber.

7. The multichannel optical coupler array of Example 5,

-   -   wherein said one of said plurality of optical fibers has a core        refractive index NcoreFiber and cladding refractive index        NcladdingFiber and said optical device has a mode with core        refractive index NcoreDevice and cladding refractive index        NcladdingDevice, and    -   wherein said N-1 is substantially equal to NcoreFiber, N-2 is        substantially equal NcladdingFiber, and N-3 is substantially        equal to (N-2)−(NcoreDevice-NcladdingDevice).

8. The multichannel optical coupler array of Example 1, wherein saidNeff1 is larger than NeffFiber and said Neff2 is smaller thanNeffDevice.

9. The multichannel optical coupler array of Example 8, wherein said oneof said plurality of optical fibers has a cladding refractive indexNcladdingFiber, and wherein said third refractive index (N-3) in atleast one of said vanishing core waveguides is lower than saidNcladdingFiber.

10. The optical coupler array of Example 8,

-   -   wherein said one of said plurality of optical fibers has a core        refractive index NcoreFiber and cladding refractive index        NcladdingFiber and said optical device has a mode with core        refractive index NcoreDevice and cladding refractive index        NcladdingDevice, and    -   wherein said N-3 is smaller than NcladdingFiber, N-2 is        substantially equal to (N-3)+(NcoreDevice-NcladdingDevice), and        N-1 is substantially equal to (N-2)+(NcoreFiber-NcladdingFiber).

11. The multichannel optical coupler array of Example 8, wherein in atleast one of said vanishing core waveguides comprises a refractive indexprofile in which:

-   -   said first refractive index (N-1),    -   said first inner core size (ICS-1),    -   said second inner core size (ICS-2),    -   said second refractive index (N-2),    -   said first outer core size (OCS-1),    -   said second outer core size (OCS-2), and    -   said third refractive index (N-3),    -   are configured to reduce at an optical fiber interface and at an        optical device interface, a sum of back reflections of the light        traveling in at least one of: in said first direction from said        plurality of optical fibers to said optical device, or in said        second direction from said optical device to said plurality of        optical fibers.

12. The multichannel optical coupler array of Example 1, wherein theoptical coupler array is configured to increase optical coupling to saidoptical device at said second end, wherein said optical device comprisesone of:

-   -   a free-space-based optical device,    -   an optical circuit having at least one input/output edge        coupling port, or    -   an optical circuit having at least one optical port comprising        vertical coupling elements.

13. The multichannel optical coupler array of Example 1, wherein theoptical coupler array is configured to increase optical coupling to saidoptical device at said second end, wherein said optical device comprisesone of:

-   -   a multi-mode optical fiber,    -   a double-clad optical fiber,    -   a multi-core optical fiber,    -   a large mode area fiber,    -   a double-clad multi-core optical fiber,    -   a standard/conventional optical fiber, or    -   a custom optical fiber.

14. The multichannel optical coupler array of Example 1, wherein theoptical coupler array is configured to increase optical coupling to saidoptical device at said second end, wherein said optical device comprisesan additional optical coupler array.

15. The multichannel optical coupler array of Example 1, whereinN-3≤N-4.

16. The multichannel optical coupler array of Example 1, whereinproximate the second end, the coupler array comprises substantially nogap between the coupler housing structure and the plurality oflongitudinal waveguides.

17. The multichannel optical coupler array of Example 1, wherein thecross sectional configuration comprises a ring surrounding saidplurality of longitudinal waveguides.

18. The multichannel optical coupler array of Example 17, wherein theplurality of longitudinal waveguides are in a hexagonal arrangement.

19. The multichannel optical coupler array of Example 17, wherein thering has a circular inner cross section.

20. The multichannel optical coupler array of Example 17, wherein thering has a non-circular inner cross section.

21. The multichannel optical coupler array of Example 17, wherein thering has a circular outer cross section.

22. The multichannel optical coupler array of Example 17, wherein thering has a non-circular outer cross section.

23. The multichannel optical coupler array of Example 1, wherein thecross sectional configuration comprises a structure with a plurality ofholes.

24. The multichannel optical coupler array of Example 23, wherein theholes are in a hexagonal arrangement.

25. The multichannel optical coupler array of Example 23, wherein theholes are in a rectangular arrangement.

26. The multichannel optical coupler array of Example 23, wherein saidplurality of holes is defined in an XY array.

27. The multichannel optical coupler array of Example 23, wherein atleast one hole has a circular cross section.

28. The multichannel optical coupler array of Example 23, wherein atleast one hole has a non-circular cross section.

29. The multichannel optical coupler array of Example 23, wherein atleast one of the holes has a different dimension than another one of theholes.

30. The multichannel optical coupler array of Example 23, wherein atleast one of the holes has a different shape than another one of theholes.

Example Set II

1. A multichannel optical coupler comprising:

-   -   an output optical coupler array; and    -   a plurality of optical fibers, wherein at least two of said        plurality of optical fibers are connected together at an end        opposite said output optical coupler array.

2. The multichannel optical coupler of Example 1, wherein the outputoptical coupler array comprises a reflector to form a Talbot cavity.

3. The multichannel optical coupler of Example 1, wherein the outputoptical coupler array comprises a pitch reducing optical fiber array.

4. The multichannel optical coupler of Example 3, wherein the outputoptical coupler array comprises:

-   -   an elongated optical element having a first end operable to        optically couple with said plurality of optical fibers and a        second end operable to optically couple with an optical device,        and comprising:        -   a common single coupler housing structure; a plurality of            longitudinal waveguides each positioned at a predetermined            spacing from one another, each having a capacity for at            least one optical mode of a predetermined mode field            profile, each embedded in said common single housing            structure proximally to said second end, wherein at least            one of said plurality of longitudinal waveguides is a            vanishing core waveguide, each said at least one vanishing            core waveguide comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having a first inner core size (ICS-1) at                said first end, and a second inner core size (ICS-2) at                said second end; an outer core, longitudinally                surrounding said inner core, having a second refractive                index (N-2), and having a first outer core size (OCS-1)                at said first end, and a second outer core size (OCS-2)                at said second end, and an outer cladding,                longitudinally surrounding said outer core, having a                third refractive index (N-3), a first cladding size at                said first end, and a second cladding size at said                second end; and wherein said common single coupler                housing structure comprises a transversely contiguous                medium having a fourth refractive index (N-4)                surrounding said plurality of longitudinal waveguides,                wherein a predetermined relative magnitude relationship                between said first, second, third and fourth refractive                indices (N-1, N-2, N-3, and N-4, respectively),                comprises the following magnitude relationship:                (N-1>N-2>N-3),    -   wherein a total volume of said medium or said common single        coupler housing structure, is greater than a total volume or all        said vanishing core waveguides inner cores and said outer cores        confined within said common single coupler housing structure,        and wherein said first inner vanishing core size (ICS-1), said        first outer core size (OCS-1), and said predetermined spacing        between said plurality of longitudinal waveguides, are        simultaneously and gradually reduced, in accordance with a        predetermined reduction profile, between said first end and said        second end along said optical element, until said second inner        vanishing core size (ICS-2) and said second outer core size        (OCS-2) are reached, wherein said second inner vanishing core        size (ICS-2) is selected to be insufficient to guide light        therethrough, and said second outer core size (OCS-2) is        selected to be sufficient to guide at least one optical mode,        such that:        -   light traveling from said first end to said second end            escapes from said inner vanishing core into said            corresponding outer core proximally to said second end, and            light traveling from said second end to said first end moves            from said outer core into said corresponding inner vanishing            core proximally to said first end.

5. The multichannel optical coupler of Example 3, wherein the outputoptical coupler array comprises:

-   -   an elongated optical element having a first end operable to        optically couple with said plurality of optical fibers, an        intermediate cross section, and a second end operable to        optically couple with an optical device, and comprising:        -   a common single coupler housing structure;        -   a plurality of longitudinal waveguides each positioned at a            predetermined spacing from one another, each having a            capacity for at least one optical mode of a predetermined            mode field profile, each embedded in said common single            housing structure proximally to said second end, wherein at            least one of said plurality of longitudinal waveguides is a            vanishing core waveguide, each said at least one vanishing            core waveguide comprising:        -   an inner vanishing core, having a first refractive index            (N-1), and having a first inner core size (ICS-1) at said            first end, an intermediate inner core size (ICS-IN) at said            intermediate cross section, and a second inner core size            (ICS-2) at said second end; an outer core, longitudinally            surrounding said inner core, having a second refractive            index (N-2), and having a first outer core size (OCS-1) at            said first end, an intermediate outer core size (OCS-IN) at            said intermediate cross section, and a second outer core            size (OCS-2) at said second end, and an outer cladding,            longitudinally surrounding said outer core, having a third            refractive index (N-3), a first cladding size at said first            end, and a second cladding size at said second end; and            wherein said common single coupler housing structure            comprises a transversely contiguous medium having a fourth            refractive index (N-4) surrounding said plurality of            longitudinal waveguides, wherein a predetermined relative            magnitude relationship between said first, second, third and            fourth refractive indices (N-1, N-2, N-3, and N-4,            respectively), comprises the following magnitude            relationship: (N-1>N-2>N-3), wherein a total volume of said            medium of said common single coupler housing structure, is            greater than a total volume of all said vanishing core            waveguides inner cores and said outer cores confined within            said common single coupler housing structure, and wherein            said first inner vanishing core size (ICS-1), said first            outer core size (OCS-1), and said predetermined spacing            between said plurality of longitudinal waveguides, are            simultaneously and gradually reduced, in accordance with a            predetermined reduction profile, between said first end and            said second end along said optical element, until said            second inner vanishing core size (ICS-2) and said second            outer core size (OCS-2) are reached, wherein said            intermediate inner vanishing core size (ICS-IN) is selected            to be insufficient to guide light therethrough, and said            intermediate outer core size (OCS-IN) is selected to be            sufficient to guide at least one optical mode, and said            second outer core size (OCS-2) is selected to be            insufficient to guide light therethrough such that:        -   light traveling from said first end to said second end            escapes from said inner vanishing core into said            corresponding outer core proximally to said intermediate            cross section, and escapes from said outer core into a            combined waveguide formed by at least two neighboring outer            cores proximally to said second end, and        -   at least one waveguide mode of light traveling from said            second end to said first end moves from the combined            waveguide formed by at least two neighboring outer cores            into said outer core proximally to said intermediate cross            section, and moves from said outer core into said            corresponding inner vanishing core proximally to said first            end.

6. The multichannel optical coupler of Example 1, wherein said pluralityof optical fibers comprises one or more gain blocks configured to allowlight amplification.

7. The multichannel optical coupler of Example 1, wherein said pluralityof optical fibers comprises at least one optical fiber not connectedwith another optical fiber at the end opposite said output opticalcoupler array.

8. The multichannel optical coupler of Example 7, wherein said at leastone optical fiber not connected with another optical fiber is configuredto form a laser cavity suitable for passive or active phase locking.

9. The multichannel optical coupler of Example 7, wherein the at leastone optical fiber not connected with another optical fiber comprises atleast one reflector, fiber Bragg grating, or modulating element.

10. A device configured to generate a single polarization mode, thedevice comprising the multichannel optical coupler of Example 1, whereinthe at least two fibers connected together comprise one or morepolarization beam splitters.

11. A device configured to generate a single polarization mode, thedevice comprising the multichannel optical coupler of Example 1, whereinthe at least two fibers connected together comprise one or moreisolators.

12. A device configured to generate a single polarization mode, thedevice comprising the multichannel optical coupler of Example 1 and oneor more polarization converters.

13. The device of Example 12, wherein the one or more polarizationconverters comprise one or more circular-to-linear or linear-to-circularconverters.

14. The multichannel optical coupler of Example 1, wherein the pluralityof optical fibers comprises at least four optical fibers.

15. The multichannel optical coupler of Example 14, wherein theplurality of optical fibers comprises at least six optical fibers.

16. The multichannel optical coupler of Example 15, wherein theplurality of optical fibers comprises at least eight optical fibers.

17. The multichannel optical coupler of Example 16, wherein theplurality of optical fibers comprises at least ten optical fibers.

18. The multichannel optical coupler of Example 1, wherein the outputoptical coupler array comprises a plurality of waveguides.

19. The multichannel optical coupler of Example 1, wherein the outputoptical coupler array comprises a plurality of cores configured tosupport at least one propagating mode.

20. The multichannel optical coupler of Example 2, wherein the reflectorcomprises a Talbot mirror.

21. The multichannel optical coupler of Example 1, wherein the outputoptical coupler array comprises at least one reflector at an endopposite the plurality of optical fibers.

22. The multichannel optical coupler of Example 1, wherein the outputoptical coupler array comprises a common reflector at an end oppositethe plurality of optical fibers.

Example Set III

1. A multichannel optical coupler array for optical coupling of aplurality of optical fibers to an optical device, comprising:

-   -   an elongated optical element having a first end operable to        optically couple with said plurality optical fibers and a second        end operable to optically couple with said optical device, and        comprising:        -   a common single coupler housing structure; a plurality of            longitudinal waveguides each positioned at a predetermined            spacing from one another, each having a capacity for at            least one optical mode of a predetermined mode field            profile, each embedded in said common single housing            structure proximally to said second end, wherein at, least            one of said plural longitudinal waveguides is a vanishing            core waveguide, each said at least one vanishing core            waveguide comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having a first inner core size (ICS-I) at                said first end, and a second inner core size (ICS-2) at                said second end; an outer core, longitudinally                surrounding said inner core, having a second refractive                index (N-2), and having a first outer core size (OCS-I)                at said first end, and a second outer core size (OCS-2)                at said second end, and an outer cladding,                longitudinally surrounding said outer core, having a                third refractive index (N-3), a first cladding size at                said first end, and a second cladding size at said                second end; and wherein said common single coupler                housing structure comprises a transversely contiguous                medium having a fourth refractive index (N-4)                surrounding said plural longitudinal waveguides, wherein                a predetermined relative magnitude relationship between                said first, second, third and fourth refractive indices                (N-1, N-2, N-3, and N-4, respectively), comprises the                following magnitude relationship: (N-1>N-2>N-3),    -   wherein a total volume of said medium or said common single        coupler housing structure, is greater than a total volume or all        said vanishing core waveguides inner cores and said outer cores        confined within said common single coupler housing structure,        and wherein said first inner vanishing core size (ICS-I), said        first outer core size (OCS-I), and said predetermined spacing        between said plural longitudinal waveguides, are simultaneously        and gradually reduced, in accordance with a predetermined        reduction profile, between said first end and said second end        along said optical element, until said second inner vanishing        core size (ICS-2) and said second outer core size (OCS-2) are        reached, wherein said second inner vanishing core size (ICS-2)        is selected to be insufficient to guide light therethrough, and        said second outer core size (OCS-2) is selected to be sufficient        to guide at least one optical mode, such that:    -   light traveling from said first end to said second end escapes        from said inner vanishing core into said corresponding outer        core proximally to said second end, and light traveling from        said second end to said first end moves from said outer core        into said corresponding inner vanishing core proximally to said        first end,    -   and wherein said common single coupler housing structure        proximally to said first end has one of the following cross        sectional configurations: a ring surrounding said plurality of        longitudinal waveguides, a transversely contiguous structure        with plurality of holes, wherein at least one said hole contains        at least one of said plurality of longitudinal waveguides.

2. A multichannel optical coupler array, comprising:

-   -   an elongated optical element having a first end and a second        end, wherein said first and second ends are operable to        optically couple with a plurality of optical fibers, an optical        device, or combinations thereof, the optical element further        comprising:        -   a coupler housing structure; and        -   a plurality of longitudinal waveguides arranged with respect            to one another, each having a capacity for at least one            optical mode, the plurality of longitudinal waveguides            embedded in said housing structure, wherein said plurality            of longitudinal waveguides comprises at least one vanishing            core waveguide, each said at least one vanishing core            waveguide, said at least one vanishing core waveguide            comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having an inner core size;            -   an outer core, longitudinally surrounding said inner                core, having a second refractive index (N-2), and having                an outer core size; and            -   an outer cladding, longitudinally surrounding said outer                core, having a third refractive index (N-3), and having                a cladding size;        -   wherein said coupler housing structure comprises a medium            having a fourth refractive index (N-4) surrounding said            plurality of longitudinal waveguides, wherein N-1>N-2>N-3,        -   wherein said inner core size, said outer core size, and            spacing between said plurality of longitudinal waveguides            reduces along said optical element from said first end to            said second end such that at said second end, said inner            core size is insufficient to guide light therethrough, and            said outer core size is sufficient to guide at least one            optical mode, and        -   wherein said coupler housing structure at a proximity to the            first end has one of the following cross sectional            configurations: a ring surrounding said plurality of            longitudinal waveguides with a gap between said ring and            said plurality of longitudinal waveguides, or a structure            with a plurality of holes, at least one hole containing at            least one of said plurality of longitudinal waveguides.

3. The optical coupler array of Example 2, wherein the coupler housingstructure comprises a common single coupler housing structure.

4. The optical coupler array of any of the preceding Examples, whereinproximate the first end, one of the plurality of longitudinal waveguidesextends outside the coupler housing structure.

5. The optical coupler array of any of the preceding Examples, whereinproximate the first end, one of the plurality of longitudinal waveguidesis disposed within the coupler housing structure and does not extendsbeyond the coupler housing structure.

6. The optical coupler array of any of the preceding Examples, whereinproximate the first end, one of the plurality of longitudinal waveguidesis disposed at an outer cross sectional boundary region of the couplerhousing structure and does not extends beyond the coupler housingstructure.

7. The optical coupler array of any of Examples 2-6, wherein the mediumis a transversely contiguous medium.

8. The optical coupler array of any of Examples 2-7, wherein a totalvolume of said medium of said coupler housing structure is greater thana total volume of all the inner and outer cores of the at least onevanishing core waveguide confined within said coupler housing structure.

9. The optical coupler array of any of Examples 2-8, wherein said innercore size, said outer core size, and spacing between said plurality oflongitudinal waveguides simultaneously and gradually reduces from saidfirst end to said second end.

10. The optical coupler array of any of the preceding Examples, whereinproximate the second end, the coupler array comprises substantially nogap between the coupler housing structure and the plurality oflongitudinal waveguides.

11. The optical coupler array of any of the preceding Examples, whereinthe one of the cross sectional configurations is the ring surroundingsaid plurality of longitudinal waveguides.

12. The optical coupler array of Example 11, wherein the plurality oflongitudinal waveguides are in a hexagonal arrangement.

13. The optical coupler array of any of Examples 11-12, wherein the ringhas a circular inner cross section.

14. The optical coupler array of any of Examples 11-12, wherein the ringhas a non-circular inner cross section.

15. The optical coupler array of Example 14, wherein the inner crosssection is hexagonal.

16. The optical coupler array of Example 14, wherein the inner crosssection is D-shaped.

17. The optical coupler array of any of Examples 11-16, wherein the ringhas a circular outer cross section.

18. The optical coupler array of any of Examples 11-16, wherein the ringhas a non-circular outer cross section.

19. The optical coupler array of Example 18, wherein the outer crosssection is hexagonal.

20. The optical coupler array of Example 18, wherein the outer crosssection is D-shaped.

21. The optical coupler array of any of Examples 1-10, wherein the oneof the cross sectional configurations is the structure with theplurality of holes.

22. The optical coupler array of Example 21, wherein the holes are in ahexagonal arrangement.

23. The optical coupler array of Example 21, wherein the holes are in arectangular arrangement.

24. The optical coupler array of Example 21, wherein said plurality ofholes is defined in an XY array.

25. The optical coupler array of any of Examples 21-24, wherein at leastone hole comprises non-waveguide material.

26. The optical coupler array of any of Examples 21-25, wherein at leastone hole has a circular cross section.

27. The optical coupler array of any of Examples 21-26, wherein at leastone hole has a non-circular cross section.

28. The optical coupler array of Example 27, wherein the non-circularcross section is D-shaped.

29. The optical coupler array of any of Examples 21-28, wherein at leastone of the holes has a different dimension than another one of theholes.

30. The optical coupler array of any of Examples 21-29, wherein at leastone of the holes has a different shape than another one of the holes.

31. The optical coupler array of any of Examples 21-30, wherein theholes are isolated.

32. The optical coupler array of any of Examples 21-30, wherein some ofthe holes are connected.

33. The optical coupler array of any of the preceding Examples, whereinthe at least one vanishing core waveguide comprises a single mode fiber.

34. The optical coupler array of any of the preceding Examples, whereinthe at least one vanishing core waveguide comprises a multi-mode fiber.

35. The optical coupler array of any of the preceding Examples, whereinthe at least one vanishing core waveguide comprises a polarizationmaintaining fiber.

36. A multichannel optical coupler array, comprising:

-   -   an elongated optical element having a first end and a second        end, wherein said first and second ends are operable to        optically couple with a plurality of optical fibers, an optical        device, or combinations thereof, the optical element further        comprising:        -   a coupler housing structure; and        -   a plurality of longitudinal waveguides arranged with respect            to one another, each having a capacity for at least one            optical mode, the plurality of longitudinal waveguides            embedded in said housing structure, wherein said plurality            of longitudinal waveguides comprises at least one vanishing            core waveguide, each said at least one vanishing core            waveguide, said at least one vanishing core waveguide            comprising:            -   an inner vanishing core having a first refractive index                (N-1), and having an inner core size;            -   an outer core, longitudinally surrounding said inner                core, having a second refractive index (N-2) and having                an outer core size; and            -   an outer cladding, longitudinally surrounding said outer                core, having a third refractive index (N-3), and having                a cladding size;    -   wherein said coupler housing structure comprises a medium having        a fourth refractive index (N-4) surrounding said plurality of        longitudinal waveguides, wherein N-1>N-2>N-3,    -   wherein said inner core size, said outer core size, and spacing        between said plurality of longitudinal waveguides reduces along        said elongated optical element from said first end to said        second end such that at said second end, said inner core size is        insufficient to guide light therethrough, and said outer core        size is sufficient to guide at least one optical mode, and    -   wherein said coupler housing structure at a proximity to the        first end has a cross sectional configuration comprising at        least one hole, the at least one hole containing at least one of        said plurality of longitudinal waveguides, wherein the hole is        larger than the at least one of said plurality of longitudinal        waveguides such that the at least one of said plurality of        longitudinal waveguides is movable with respect to the coupler        housing structure in a lateral direction.

37. The optical coupler array of Example 36, wherein the coupler housingstructure comprises a common single coupler housing structure.

38. The optical coupler array of any of Examples 36-37, whereinproximate the first end, one of the plurality of longitudinal waveguidesextends outside the coupler housing structure.

39. The optical coupler array of any of Examples 36-38, whereinproximate the first end, one of the plurality of longitudinal waveguidesis disposed within the coupler housing structure.

40. The optical coupler array of any of Examples 36-39, wherein themedium is a transversely contiguous medium.

41. The optical coupler array of any of Examples 36-40, wherein a totalvolume of said medium of said coupler housing structure is greater thana total volume of all the inner and outer cores of the at least onevanishing core waveguide confined within said coupler housing structure.

42. The optical coupler array of any of Examples 36-41, wherein saidinner core size, said outer core size, and spacing between saidplurality of longitudinal waveguides simultaneously and graduallyreduces from said first end to said second end.

43. The optical coupler array of any of Examples 36-42, whereinproximate the second end, the coupler array comprises substantially nogap between the coupler housing structure and the plurality oflongitudinal waveguides.

44. The optical coupler array of any Examples 36-43, wherein the atleast one hole comprises a single hole and the at least one of saidplurality of longitudinal waveguides comprises a plurality oflongitudinal waveguides.

45. The optical coupler array of Example 44, wherein the plurality oflongitudinal waveguides are in a hexagonal arrangement.

46. The optical coupler array of any of Examples 44-45, wherein thesingle hole as a circular cross section.

47. The optical coupler array of any of Examples 44-45, wherein thesingle hole has a non-circular cross section.

48. The optical coupler array of Example 47, wherein the non-circularcross section is hexagonal.

49. The optical coupler array of Example 47, wherein the non-circularcross section is D-shaped.

50. The optical coupler array of any of Examples 44-49, wherein thecoupler housing structure has a circular outer cross section.

51. The optical coupler array of any of Examples 44-49, wherein thecoupler housing structure has a non-circular outer cross section.

52. The optical coupler array of Example 51, wherein the outer crosssection is hexagonal.

53. The optical coupler array of Example 51, wherein the outer crosssection is D-shaped.

54. The optical coupler array of any of Examples 36-43, wherein the atleast one hole comprises a plurality of holes.

55. The optical coupler array of Example 54, wherein the plurality ofholes are in a hexagonal arrangement.

56. The optical coupler array of Example 54, wherein the plurality ofholes are in a rectangular arrangement.

57. The optical coupler array of Example 54, wherein said plurality ofholes is defined by an XY array.

58. The optical coupler array of any of Examples 54-57, wherein one ormore of the plurality of holes comprises non-waveguide material.

59. The optical coupler array of any of Examples 54-58, wherein one ormore of the plurality of holes has a circular cross section.

60. The optical coupler array of any of Examples 54-59, wherein one ormore of the plurality of holes has a non-circular cross section.

61. The optical coupler array of Example 60, wherein the non-circularcross section is D-shaped.

62. The optical coupler array of any of Examples 54-61, wherein one ormore of the plurality of holes has a different dimension than anotherone of the holes.

63. The optical coupler array of any of Examples 54-62, wherein one ormore of the plurality of holes has a different shape than another one ofthe holes.

64. The optical coupler array of any of Examples 54-63, wherein theholes are isolated.

65. The optical coupler array of any of Examples 54-63, wherein some ofthe holes are connected.

66. The optical coupler array of any of Examples 54-65, wherein the atleast one vanishing core waveguide comprises a single mode fiber.

67. The optical coupler array of any of Examples 54-66, wherein the atleast one vanishing core waveguide comprises a multi-mode fiber.

68. The optical coupler array of any of Examples 54-67, wherein the atleast one vanishing core waveguide comprises a polarization maintainingfiber.

Example Set IV

1. A multichannel optical coupler array for optical coupling a pluralityof optical fibers to an optical device, comprising:

-   -   an elongated optical element having a first end operable to        optically couple with said plurality optical fibers and a second        end operable to optically couple with said optical device, and        comprising:    -   a common single coupler housing structure; a plurality of        longitudinal waveguides each positioned at a predetermined        spacing from one another, each having a capacity for at least        one optical mode of a predetermined mode field profile, each        embedded in said common single housing structure, wherein at,        least one of said plural longitudinal waveguides is a vanishing        core waveguide, each said at least one vanishing core waveguide        comprising:    -   an inner vanishing core, having a first refractive index (N-1),        and having a first inner core size (ICS-I) at said first end,        and a second inner core size (ICS-2) at said second end; an        outer core, longitudinally surrounding said inner core, having a        second refractive index (N-2), and having a first outer core        size (OCS-I) at said first end, and a second outer core size        (OCS-2) at said second end, and an outer cladding,        longitudinally surrounding said outer core, having a third        refractive index (N-3), a first cladding size at said first end,        and a second cladding size at said second end; and wherein said        common single coupler housing structure comprises a transversely        contiguous medium having a fourth refractive index (N-4)        surrounding said plural longitudinal waveguides, wherein a        predetermined relative magnitude relationship between said        first, second, third and fourth refractive indices (N-1, N-2,        N-3, and N-4, respectively), comprises the following magnitude        relationship: (N-1>N-2>N-3),    -   wherein a total volume of said medium or said common single        coupler housing structure, is greater than a total volume or all        said vanishing core waveguides inner cores and said outer cores        confined within said common single coupler housing structure,        and wherein said first inner vanishing core size (ICS-I), said        first outer core size (OCS-I), and said predetermined spacing        between said plural longitudinal waveguides, are simultaneously        and gradually reduced, in accordance with a predetermined        reduction profile, between said first end and said second end        along said optical element, until said second inner vanishing        core size (ICS-2) and said second outer core size (OCS-2) are        reached, wherein said second inner vanishing core size (ICS-2)        is selected to be insufficient to guide light therethrough, and        said second outer core size (OCS-2) is selected to be sufficient        to guide at least one optical mode, such that:    -   light traveling from said first end to said second end escapes        from said inner vanishing core into said corresponding outer        core proximally to said second end, and light traveling from        said second end to said first end moves from said outer core        into said corresponding inner vanishing core proximally to said        first end,    -   and wherein said common single coupler housing structure at a        close proximity to the first end has one of the following cross        sectional configurations: a ring surrounding said plurality of        longitudinal waveguides, a contiguous structure with plurality        of holes, at least one hole containing at least one of said        plurality of longitudinal waveguides.        2. A multichannel optical coupler array for optical coupling a        plurality of optical fibers to an optical device, comprising:    -   an elongated optical element having a first end operable to        optically couple with said plurality optical fibers and a second        end operable to optically couple with said optical device, and        comprising:    -   a coupler housing structure; a plurality of longitudinal        waveguides each positioned at a spacing from one another, each        having a capacity for at least one optical mode, each embedded        in said housing structure, wherein at, least one of said plural        longitudinal waveguides is a vanishing core waveguide, each said        at least one vanishing core waveguide comprising:    -   an inner vanishing core, having a first refractive index (N-1),        and having a first inner core size (ICS-I) at said first end,        and a second inner core size (ICS-2) at said second end; an        outer core, longitudinally surrounding said inner core, having a        second refractive index (N-2), and having a first outer core        size (OCS-I) at said first end, and a second outer core size        (OCS-2) at said second end, and an outer cladding,        longitudinally surrounding said outer core, having a third        refractive index (N-3), a first cladding size at said first end,        and a second cladding size at said second end; and wherein said        coupler housing structure comprises a medium having a fourth        refractive index (N-4) surrounding said plural longitudinal        waveguides, wherein a relative magnitude relationship between        said first, second, third and fourth refractive indices (N-1,        N-2, N-3, and N-4, respectively), comprises the following        magnitude relationship: (N-1>N-2>N-3),    -   wherein said first inner vanishing core size (ICS-I), said first        outer core size (OCS-I), and said spacing between said plural        longitudinal waveguides, reduces between said first end and said        second end along said optical element, until said second inner        vanishing core size (ICS-2) and said second outer core size        (OCS-2) are reached, wherein said second inner vanishing core        size (ICS-2) is insufficient to guide light therethrough, and        said second outer core size (OCS-2) is sufficient to guide at        least one optical mode, such that:    -   light traveling from said first end to said second end escapes        from said inner vanishing core into said corresponding outer        core proximally to said second end, and light traveling from        said second end to said first end moves from said outer core        into said corresponding inner vanishing core proximally to said        first end,    -   and wherein said coupler housing structure at a close proximity        to the first end has one of the following cross sectional        configurations: a ring surrounding said plurality of        longitudinal waveguides, or a structure with plurality of holes,        at least one hole containing at least one of said plurality of        longitudinal waveguides.

Example Set V

1. A multichannel optical coupler array for optical coupling of aplurality of optical fibers to an optical device, comprising:

-   -   an elongated optical element having a first end operable to        optically couple with said plurality optical fibers, an        intermediate cross section, and a second end operable to        optically couple with said optical device, and comprising:        -   a common single coupler housing structure; a plurality of            longitudinal waveguides each positioned at a predetermined            spacing from one another, each having a capacity for at            least one optical mode of a predetermined mode field            profile, each embedded in said common single housing            structure proximally to said second end, wherein at least            one of said plural longitudinal waveguides is a vanishing            core waveguide, each said at least one vanishing core            waveguide comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having a first inner core size (ICS-I) at                said first end, an intermediate inner core size (ICS-IN)                at said intermediate cross section, and a second inner                core size (ICS-2) at said second end; an outer core,                longitudinally surrounding said inner core, having a                second refractive index (N-2), and having a first outer                core size (OCS-I) at said first end, an intermediate                outer core size (OCS-IN) at said intermediate cross                section, and a second outer core size (OCS-2) at said                second end, and an outer cladding, longitudinally                surrounding said outer core, having a third refractive                index (N-3), a first cladding size at said first end,                and a second cladding size at said second end; and                wherein said common single coupler housing structure                comprises a transversely contiguous medium having a                fourth refractive index (N-4) surrounding said plural                longitudinal waveguides, wherein a predetermined                relative magnitude relationship between said first,                second, third and fourth refractive indices (N-1, N-2,                N-3, and N-4, respectively), comprises the following                magnitude relationship: (N-1>N-2>N-3), wherein a total                volume of said medium or said common single coupler                housing structure, is greater than a total volume or all                said vanishing core waveguides inner cores and said                outer cores confined within said common single coupler                housing structure, and wherein said first inner                vanishing core size (ICS-I), said first outer core size                (OCS-I), and said predetermined spacing between said                plural longitudinal waveguides, are simultaneously and                gradually reduced, in accordance with a predetermined                reduction profile, between said first end and said                second end along said optical element, until said second                inner vanishing core size (ICS-2) and said second outer                core size (OCS-2) are reached, wherein said intermediate                inner vanishing core size (ICS-IN) is selected to be                insufficient to guide light therethrough, and said                intermediate outer core size (OCS-IN) is selected to be                sufficient to guide at least one optical mode, and said                second outer core size (OCS-2) is selected to be                insufficient to guide light therethrough such that:            -   light traveling from said first end to said second end                escapes from said inner vanishing core into said                corresponding outer core proximally to said intermediate                cross section, and escapes from said outer core into a                combined waveguide formed by at least two neighboring                outer cores proximally to said second end, and            -   at least one waveguide mode of light traveling from said                second end to said first end moves from the combined                waveguide formed by at least two neighboring outer cores                into said outer core proximally to said intermediate                cross section, and moves from said outer core into said                corresponding inner vanishing core proximally to said                first end,    -   and wherein said common single coupler housing structure        proximally to said first end has a cross sectional configuration        comprising a transversely contiguous structure with at least one        hole, wherein the at least one hole contains at least one of        said plurality of longitudinal waveguides creating a gap between        the coupler housing structure and the at least one of said        plurality of longitudinal waveguides.

2. A multichannel optical coupler array comprising:

-   -   an elongated optical element having a first end, an intermediate        cross section, and a second end, and comprising:        -   a coupler housing structure; a plurality of longitudinal            waveguides each positioned at a spacing from one another,            each having a capacity for at least one optical mode, each            disposed in said housing structure, wherein at least one of            said plural longitudinal waveguides is a vanishing core            waveguide, each said at least one vanishing core waveguide            comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having a first inner core size (ICS-I) at                said first end, an intermediate inner core size (ICS-IN)                at said intermediate cross section, and a second inner                core size (ICS-2) at said second end; an outer core,                longitudinally surrounding said inner core, having a                second refractive index (N-2), and having a first outer                core size (OCS-I) at said first end, an intermediate                outer core size (OCS-IN) at said intermediate cross                section, and a second outer core size (OCS-2) at said                second end, and an outer cladding, longitudinally                surrounding said outer core, having a third refractive                index (N-3), a first cladding size at said first end,                and a second cladding size at said second end; and                wherein said coupler housing structure comprises a                medium having a fourth refractive index (N-4)                surrounding said plural longitudinal waveguides, wherein                a relative magnitude relationship between said first,                second, third and fourth refractive indices (N-1, N-2,                N-3, and N-4, respectively), comprises the following                magnitude relationship: (N-1>N-2>N-3), and wherein said                first inner vanishing core size (ICS-I), said first                outer core size (OCS-I), and said spacing between said                plural longitudinal waveguides are reduced between said                first end and said second end along said optical                element, wherein said intermediate inner vanishing core                size (ICS-IN) is insufficient to guide light                therethrough, and said intermediate outer core size                (OCS-IN) is sufficient to guide at least one optical                mode, and said second outer core size (OCS-2) is                insufficient to guide light therethrough such that:            -   light traveling from said first end to said second end                escapes from said inner vanishing core into said                corresponding outer core proximally to said intermediate                cross section, and escapes from said outer core into a                combined waveguide formed by at least two neighboring                outer cores proximally to said second end, and            -   at least one waveguide mode of light traveling from said                second end to said first end moves from the combined                waveguide formed by at least two neighboring outer cores                into said outer core proximally to said intermediate                cross section, and moves from said outer core into said                corresponding inner vanishing core proximally to said                first end.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference characters denote correspondingor similar elements throughout the various figures:

FIG. 1A is a schematic diagram of a side view of a first exampleembodiment of an optical fiber coupler array, which comprises at leastone vanishing core waveguide (VC waveguide), illustrated therein by wayof example as a single VC waveguide, and at least one Non-VC waveguide,illustrated therein by way of example as a plurality of Non-VCwaveguides, disposed symmetrically proximally to the example single VCwaveguide;

FIG. 1B is a schematic diagram of a side view of a second exampleembodiment of an optical fiber coupler array, which comprises at leastone vanishing core waveguide (VC waveguide), illustrated therein by wayof example as a single VC waveguide, and at least one Non-VC waveguide,illustrated therein by way of example as a single Non-VC waveguide,disposed in parallel proximity to the example single VC waveguide, wherea portion of the optical fiber coupler array has been configured tocomprise a higher channel-to-channel spacing magnitude at its second(smaller) end than the corresponding channel-to-channel spacingmagnitude at the second end of the optical fiber coupler array of FIG.1A;

FIG. 1C is a schematic diagram of a side view of a third exampleembodiment of an optical fiber coupler array, which comprises aplurality of VC waveguides, and a plurality of Non-VC waveguides,disposed longitudinally and asymmetrically to one another, and where atleast a portion of the plural Non-VC waveguides are of different typesand/or different characteristics;

FIG. 1D is a schematic diagram of a side view of a fourth exampleembodiment of an optical fiber coupler array, configured for fan-in andfan-out connectivity and comprising a pair of optical fiber couplercomponents with a multi-core optical fiber element connected between thesecond (smaller sized) ends of the two optical fiber coupler components;

FIG. 2A is a schematic diagram of a side view of a fifth exampleembodiment of an optical fiber coupler array, which comprises aplurality of longitudinally proximal VC waveguides at least partiallyembedded in a single common housing structure, wherein each plural VCwaveguide is spliced, at a particular first splice location, to acorresponding elongated optical device (such as an optical fiber), atleast a portion of which extends outside the single common housingstructure by a predetermined length, and wherein each particular firstsplice location is disposed within the single common housing structure;

FIG. 2B is a schematic diagram of a side view of a sixth exampleembodiment of an optical fiber coupler array, which comprises aplurality of longitudinally proximal VC waveguides at least partiallyembedded in a single common housing structure, wherein each plural VCwaveguide is spliced, at a particular second splice location, to acorresponding elongated optical device (such as an optical fiber), atleast a portion of which extends outside the single common housingstructure by a predetermined length, and wherein each particular secondsplice location is disposed at an outer cross-sectional boundary regionof the single common housing structure;

FIG. 2C is a schematic diagram of a side view of a seventh exampleembodiment of an optical fiber coupler array, which comprises aplurality of longitudinally proximal VC waveguides at least partiallyembedded in a single common housing structure, wherein each plural VCwaveguide is spliced, at a particular third splice location, to acorresponding elongated optical device (such as an optical fiber), atleast a portion of which extends outside the single common housingstructure by a predetermined length, and wherein each particular thirdsplice location is disposed outside the single common housing structure;

FIG. 2D is a schematic diagram of a side view of an alternativeembodiment of an optical fiber coupler array, comprising a plurality oflongitudinally proximal VC waveguides at least partially embedded in asingle common housing structure, that is configured at its second end,to increase, improve, and/or optimize optical coupling to afree-space-based optical device, wherein a free-space-based device mayinclude (1) a standalone device, e.g., a lens followed by other opticalcomponents as shown in FIG. 2D, or (2) a device, which is fusionspliceable to the second coupler's end, e.g. a coreless glass element,which can serve as an end cup for power density redaction at theglass-air interface, or as a Talbot mirror for phase synchronization ofcoupler's waveguides in a Talbot cavity geometry;

FIG. 3A is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler arrays of FIGS. 1Dto 2D, above, and optionally comprising a fiducial element operable toprovide a visual identification of waveguide arrangement/characteristics(such as alignment), which may be disposed in one of several categoriesof cross-sectional regions;

FIG. 3B is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 1A,above, in which at least one VC waveguide, illustrated therein by way ofexample as a single VC waveguide, is positioned along a centrallongitudinal axis of the single common housing structure, and surroundedby a plurality of parallel proximal symmetrically positioned Non-VCwaveguides;

FIG. 3C is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 3Babove, in which a volume of the single common housing structure mediumsurrounding the sections of all of the waveguides embedded therein,exceeds a total volume of the inner and outer cores of the section ofthe VC waveguide that is embedded within the single common housingstructure;

FIG. 3D is a schematic diagram of a cross-sectional view of a secondalternative embodiment of the optical fiber coupler array of FIG. 3Babove, in which the at least one VC waveguide positioned along thecentral longitudinal axis of the single common housing structurecomprises a plurality of VC waveguides, and wherein a volume of thesingle common housing structure medium surrounding the sections of allof the waveguides embedded therein, exceeds a total volume of the innerand outer cores of the sections of the plural VC waveguides that areembedded within the single common housing structure;

FIG. 3E is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 3D,further comprising a central waveguide channel operable to provideoptical pumping functionality therethrough;

FIG. 3F is a schematic diagram of a cross-sectional view of a secondalternative embodiment of the optical fiber coupler array of FIG. 3D, inwhich the VC waveguide that is positioned along the central longitudinalaxis of the single common housing structure, is of a different type,and/or comprises different characteristics from the remaining plural VCwaveguides, which, if selected to comprise enlarged inner cores, may beadvantageously utilized for increasing or optimizing optical coupling todifferent types of optical pump channels of various optical devices;

FIG. 3G is a schematic diagram of a cross-sectional view of a thirdalternative embodiment of the optical fiber coupler array of FIG. 3Babove, in which at least one VC waveguide, illustrated therein by way ofexample as a single VC waveguide, is positioned as a side-channel,off-set from the central longitudinal axis of the single common housingstructure, such that this embodiment of the optical fiber coupler arraymay be readily used as a fiber optical amplifier and or a laser, whenspliced to a double-clad optical fiber having a non-concentric core forimproved optical pumping efficiency;

FIG. 3H is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 3G,above, in which the at least one VC waveguide, illustrated therein byway of example as a side-channel off-center positioned single VCwaveguide, comprises polarization maintaining properties and comprises apolarization axis that is aligned with respect to its transverseoff-center location;

FIG. 3I is a schematic diagram of a cross-sectional view of a fourthalternative embodiment of the optical fiber coupler array of FIG. 3B,above, wherein each of the centrally positioned single VC waveguide, andthe plural Non-VC waveguides, comprises polarization maintainingproperties (shown by way of example only as being induced by rod stressmembers and which may readily and alternately be induced by variousother stress or equivalent designs), and a corresponding polarizationaxis, where all of the polarization axes are aligned to one another;

FIG. 3J is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 3I,above, in which the polarization maintaining properties of all of thewaveguides result only from a non-circular cross-sectional shape of eachwaveguide's core (or outer core in the case of the VC waveguide), shownby way of example only as being at least in part elliptical, andoptionally comprising at least one waveguide arrangement indicationelement, positioned on an outer region of the single common housingstructure, representative of the particular cross-sectional geometricarrangement of the optical coupler array's waveguides, such that aparticular cross-sectional geometric waveguide arrangement may bereadily identified from at least one of a visual and physical inspectionof the single common coupler housing structure, the waveguidearrangement indication element being further operable to facilitatepassive alignment of a second end of the optical coupler array to atleast one optical device;

FIG. 3K is a schematic diagram of a cross-sectional view of a fifthalternative embodiment of the optical fiber coupler array of FIG. 3B,above, wherein the centrally positioned single VC waveguide, comprisespolarization maintaining properties (shown by way of example only asbeing induced by rod stress members and which may readily andalternately be induced by various other stress or equivalent designs),and a corresponding polarization axis, and optionally comprising aplurality of optional waveguide arrangement indication elements of thesame or of a different type, as described in connection with FIG. 3J;

FIG. 3L is a schematic diagram of a cross-sectional view of a secondalternative embodiment of the optical fiber coupler array of FIG. 3I,above, in which the single common housing structure comprises a crosssection having a non-circular geometric shape (shown by way of exampleas a hexagon), and in which the polarization axes of the waveguides arealigned to one another and to the single common housing structurecross-section's geometric shape, and optionally further comprises awaveguide arrangement indication element, as described in connectionwith FIG. 3J;

FIG. 4 is a schematic isometric view diagram illustrating an exampleconnection of a second end (i.e. “tip”) of the optical fiber couplerarray, in the process of connecting to plural vertical coupling elementsof an optical device in a proximal open air optical coupling alignmentconfiguration, that may be readily shifted into a butt-coupledconfiguration through full physical contact of the optical fiber couplerarray second end and the vertical coupling elements;

FIG. 5 is a schematic isometric view diagram illustrating an exampleconnection of a second end (i.e. “tip”) of the optical fiber couplerarray connected to plural edge coupling elements of an optical device ina butt-coupled configuration, that may be readily shifted into one ofseveral alternative coupling configurations, including a proximal openair optical coupling alignment configuration, and or an angled alignmentcoupling configuration;

FIG. 6 is a schematic diagram of a cross-sectional view of a previouslyknown optical fiber coupler having various drawbacks and disadvantagesreadily overcome by the various embodiments of the optical fiber couplerarray of FIGS. 1A to 5; and

FIG. 7 is a schematic diagram, in various views, of a flexible pitchreducing optical fiber array (PROFA).

FIG. 8 is a schematic diagram of a cross-sectional view of an exampleconfiguration of the housing structure at a proximity to a first end ofthe optical coupler array. The cross-sectional view is orthogonal to thelongitudinal direction or length of the optical coupler array.

FIG. 9 is a schematic diagram of a cross-sectional view of anotherexample configuration of the housing structure at a proximity to a firstend of the optical coupler array.

FIG. 10 and FIG. 11 are schematic diagrams, in various views, ofadditional example optical coupler arrays.

FIG. 12 is a schematic diagram of an example multichannel opticalcoupler that can be used in coherent or incoherent beam combiningapplications.

FIG. 13 is a schematic diagram of an example multichannel opticalcoupler having a single polarization mode output.

FIG. 14 and FIG. 15 are schematic graph diagrams showing various examplerefractive index profiles, each comprising a different back reflectionloss reduction scenario corresponding to a particular coupler arrayconfiguration.

DETAILED DESCRIPTION

Various implementations described herein provide improved fiber arrays,e.g., fiber arrays used in coherent or incoherent beam combiningapplications. Some embodiments can address drawbacks of other beamcombining devices, such as the drawbacks from (1) use of back reflectorsor fiber Bragg gratings (FBGs) as terminations of individual channels,(2) complex active length adjustment for phase locking, and (3)suppressing of competing supermodes. In addition, some embodiments maybe useful in creating a single polarization mode output from the fiberarray.

In some instances, improved cross sectional (or transverse) positioningof waveguides is desirable in many multichannel optical coupler arrays.In the present disclosure, some embodiments of the housing structure(e.g., a common single coupler housing structure in some cases) canallow for self-aligning waveguide arrangement at a close proximity to afirst end (e.g., hexagonal close packed arrangement in a housingstructure having circular (as shown in FIG. 8) or hexagonal inner crosssection) and improved (precise or near precise in some cases) crosssectional positioning of the waveguides at a second end.

Packaging of photonic integrated circuits (PICs) with low verticalprofile (perpendicular to the PIC plane) can also be desirable for avariety of applications, including optical communications and sensing.While this is easily achievable for edge couplers, surface couplers mayrequire substantial vertical length.

Accordingly, it may be advantageous to provide various embodiments of apitch reducing optical fiber array (PROFA)-based flexible optical fiberarray component that may be configured and possibly optimized tocomprise a structure that maintains all channels discretely withsufficiently low crosstalk, while providing enough flexibility toaccommodate low profile packaging. It may further be desirable toprovide a PROFA-based flexible optical fiber array component comprisinga flexible portion to provide mechanical isolation of a “PROFA-PICinterface” from the rest of the PROFA, resulting in increased stabilitywith respect to environmental fluctuations, including temperaturevariations and mechanical shock and vibration. It may be additionallydesirable to provide a PROFA-based flexible optical fiber arraycomprising multiple coupling arrays, each having multiple opticalchannels, combined together to form an optical multi-port input/output(TO) interface.

Certain embodiments are directed to an optical fiber coupler arraycapable of providing a low-loss, high-coupling coefficient interfacewith high accuracy and easy alignment between a plurality of opticalfibers (or other optical devices) with a first channel-to-channelspacing, and an optical device having a plurality of waveguideinterfaces with a second, smaller channel-to-channel spacing.Advantageously, in various embodiments, each of a larger size end and asmaller size end of the optical fiber coupler array is configurable tohave a correspondingly different (i.e., larger vs. smaller)channel-to-channel spacing, where the respective channel-to-channelspacing at each of the optical coupler array's larger and smaller endsmay be readily matched to a corresponding respective firstchannel-to-channel spacing of the plural optical fibers at the largeroptical coupler array end, and to a second channel-to-channel spacing ofthe optical device plural waveguide interfaces at the smaller opticalcoupler array end.

In various embodiments thereof, the optical coupler array includes aplurality of waveguides (at least one of which may optionally bepolarization maintaining), that comprises at least one gradually reduced“vanishing core fiber”, at least in part embedded within a commonhousing structure. Alternatively, in various additional embodimentsthereof, the coupler array may be configured for utilization with atleast one of an optical fiber amplifier and an optical fiber laser.

Each of the various embodiments of the optical coupler arrayadvantageously comprises at least one “vanishing core” (VC) fiberwaveguide, described, for example, below in connection with a VCwaveguide 30A of the optical coupler array 10A of FIG. 1A.

It should also be noted that the term “optical device” as generally usedherein, applies to virtually any single channel or multi-channel opticaldevice, or to any type of optical fiber, including, but not beinglimited to, standard/conventional optical fibers. For example, opticaldevices with which the coupler array may advantageously couple mayinclude, but are not limited to, one or more of the following:

-   -   a free-space-based optical device,    -   an optical circuit having at least one input/output edge        coupling port,    -   an optical circuit having at least one optical port comprising        vertical coupling elements,    -   a multi-mode (MM) optical fiber,    -   a double-clad optical fiber,    -   a multi-core (MC) optical fiber,    -   a large mode area (LMA) fiber,    -   a double-clad multi-core optical fiber,    -   a standard/conventional optical fiber,    -   a custom optical fiber, and/or    -   an additional optical coupler array.

In addition, while the term “fusion splice” is utilized in the variousdescriptions of the example embodiments of the coupler array providedbelow, in reference to interconnections between various optical couplerarray components, and connections between various optical coupler arraycomponents and optical device(s), it should be noted, that any otherform of waveguide or other coupler array component connectivitytechnique or methodology may be readily selected and utilized as amatter of design choice or necessity, without departing from the spiritof the invention, including but not limited to mechanical connections.

Referring now to FIG. 1A, a first example embodiment of an optical fibercoupler array is shown as an optical coupler array 10A, which comprisesa common housing structure 14A (described below), at least one VCwaveguide, shown in FIG. 1A by way of example, as a single VC waveguide30A, and at least one Non-VC waveguide, shown in FIG. 1A by way ofexample, as a pair of Non-VC waveguides 32A-1, 32A-2, each positionedsymmetrically proximally to one of the sides of the example single VCwaveguide 30A, wherein the section of the VC waveguide 30A, locatedbetween positions B and D of FIG. 1A is embedded in the common housingstructure 14A.

Before describing the coupler array 10A and its components in greaterdetail, it would be useful to provide a detailed overview of the VCwaveguide 30A, the example embodiments and alternative embodiments ofwhich, are advantageously utilized in each of the various embodiments ofthe coupler arrays of FIGS. 1A to 5.

The VC waveguide 30A has a larger end (proximal to position B shown inFIG. 1A), and a tapered, smaller end (proximal to position C shown inFIG. 1A), and comprises an inner core 20A (comprising a material with aneffective refractive index of N-1), an outer core 22A (comprising amaterial with an effective refractive index of N-2, smaller than N-1),and a cladding 24A (comprising a material with an effective refractiveindex of N-3, smaller than N-2).

Advantageously, the outer core 22A serves as the effective cladding atthe VC waveguide 30A large end at which the VC waveguide 30A supports“M1” spatial propagating modes within the inner core 20A, where M1 islarger than 0. The indices of refraction N-1 and N-2, are preferablychosen so that the numerical aperture (NA) at the VC waveguide 30A largeend matches the NA of an optical device (e.g. an optical fiber) to whichit is connected (such as an optical device 34A-1, for example,comprising a standard/conventional optical fiber connected to the VCwaveguide 30A at a connection position 36A-1 (e.g., by a fusion splice,a mechanical connection, or by other fiber connection designs), whilethe dimensions of the inner and outer cores (20A, 22A), are preferablychosen so that the connected optical device (e.g., the optical device34A-1), has substantially the same mode field dimensions (MFD). Here andbelow we use mode field dimensions instead of commonly used mode fielddiameter (also MFD) due to the case that the cross section of the VC orNon-VC waveguides may not be circular, resulting in a non-circular modeprofile. Thus, the mode field dimensions include both the mode size andthe mode shape and equal to the mode field diameter in the case of acircularly symmetrical mode.

During fabrication of the coupler array 10A from an appropriatelyconfigured preform (comprising the VC waveguide 30A preform having thecorresponding inner and outer cores 20A, 22A, and cladding 24A), as thecoupler array 10A preform is tapered in accordance with at least onepredetermined reduction profile, the inner core 20A becomes too small tosupport all M1 modes. The number of spatial modes, supported by theinner core at the second (tapered) end is M2, where M2<M1. In the caseof a single mode waveguide, where M1=1 (corresponding to 2 polarizationmodes), M2=0, meaning that inner core is too small to support lightpropagation. The VC waveguide 30A then acts as if comprised a fiber witha single core of an effective refractive index close to N-2, surroundedby a cladding of lower index N-3.

During fabrication of the coupler array 10A, a channel-to-channelspacing S-1 at the coupler array 10A larger end (at position B, FIG.1A), decreases in value to a channel-to-channel spacing S-2 at thecoupler array 10A smaller end (at position C, FIG. 1A), in proportion toa draw ratio selected for fabrication, while the MFD value (or theinversed NA value of the VC waveguide 30A) can be either reduced,increased or preserved depending on a selected differences in refractiveindices, (N-1−N-2) and (N-2−N-3), which depends upon the desiredapplication for the optical coupler array 10A, as described below.

The capability of independently controlling the channel-to-channelspacing and the MFD values at each end of the optical coupler array is ahighly advantageous feature of certain embodiments. Additionally, thecapability to match MFD and NA values through a corresponding selectionof the sizes and shapes of inner 20A and outer 22A cores and values ofN-1, N-2, and N-3, makes it possible to utilize the optical couplerarray to couple to various waveguides without the need to use a lens.

In various embodiments thereof, the property of the VC waveguidepermitting light to continue to propagate through the waveguide corealong the length thereof when its diameter is significantly reduced,advantageously, reduces optical loss from interfacial imperfection orcontamination, and allows the use of a wide range of materials for amedium 28A of the common housing structure 14A (described below),including, but not limited to:

-   -   (a) non-optical materials (since the light is concentrated        inside the waveguide core),    -   (b) absorbing or scattering materials or materials with        refractive index larger than the refractive index of        standard/conventional fibers for reducing or increasing the        crosstalk between the channels, and    -   (c) pure-silica (e.g., the same material as is used in most        standard/conventional fiber claddings, to facilitate splicing to        multi-core, double-clad, or multi-mode fiber.

Preferably, in accordance with certain embodiments, the desired relativevalues of NA-1 and NA-2 (each at a corresponding end of the couplerarray 10A, for example, NA-1 corresponding to the coupler array 10Alarge end, and NA-2 corresponding to the coupler array 10A small end),and, optionally, the desired value of each of NA-1 and NA-2), may bedetermined by selecting the values of the refractive indices N1, N2, andN3 of the coupler array 10A, and configuring them in accordance with atleast one of the following relationships, selected based on the desiredrelative numerical aperture magnitudes at each end of the coupler array10A:

Desired NA-1/NA-2 Corresponding Relationship Relative Magnitude bet. N1,N2, N3 NA-1 (lrg. end) > NA-2 (sm. end) (N1-N2 > N2-N3) NA-1 (lrg. end)= NA-2 (sm. end) (N1-N2 = N2-N3) NA-1 (lrg. end) < NA-2 (sm. end) (N1-N2< N2-N3)

Commonly the NA of any type of fiber is determined by the followingexpression:NA=√{square root over (n _(core) ² −n _(clad) ²)},where n_(core) and n_(clad) are the refractive indices of fiber core andcladding respectively.

It should be noted that when the above expression is used, theconnection between the NA and the acceptance angle of the fiber is onlyan approximation. In particular, fiber manufacturers often quote “NA”for single-mode (SM) fibers based on the above expression, even thoughthe acceptance angle for a single-mode fiber is quite different andcannot be determined from the indices of refraction alone.

In accordance with certain embodiments, as used herein, the various NAvalues are preferably determined utilizing effective indices ofrefraction for both n_(core), and n_(cladding), because the effectiveindices determine the light propagation and are more meaningful in thecase of structured waveguides utilized in various embodiments. Also, atransverse refractive index profile inside a waveguide may not be flat,but rather varying around the value N1, N2, N3, or N4. In addition, thetransition between regions having refractive indices N1, N2, N3, and N4may not be as sharp as a step function due to dopant diffusion or someother intentional or non-intentional factors, and may be a smoothfunction, connecting the values of N1, N2, N3, and N4. Coupling designor optimization may involve changing both the values of N1, N2, N3, andN4 and the sizes and shapes of the regions having respective indices.

Returning now to FIG. 1A, the common coupling structure 14A, comprisesthe medium 28A, in which the section of the VC waveguide 30A locatedbetween positions B and D of FIG. 1A is embedded, and which may include,but is not limited to, at least one of the following materials:

-   -   a material, having properties prohibiting propagation of light        therethrough,    -   a material having light-absorbing optical properties,    -   a material having light scattering optical properties,    -   a material having optical properties selected such that said        fourth refractive index (N-4) is greater than said third        refractive index (N-3), and/or    -   a material having optical properties selected such that said        fourth refractive index (N-4) is substantially equal to said        third refractive index (N-3).

At the optical coupler array 10A large end (proximally to position B inFIG. 1A), the VC waveguide 30A is spliced, at a particular splicelocation 36A-1 (shown by way of example as positioned inside the commonhousing structure 14A), to a corresponding respective elongated opticaldevice 34A-1 (for example, such as an optical fiber), at least a portionof which extends outside the common housing structure 14A by apredetermined length 12A, while the Non-VC waveguides 32A-1, 32A-2 arespliced, at particular splice locations 36A-2, 36A-3, respectively(disposed outside of the common housing structure 14A), to correspondingrespective elongated optical devices 34A-2, 34A-3 (such as opticalfibers), and extending outside the common housing structure 14A by apredetermined length 12A.

Optionally, the coupler array 10A may also include a substantiallyuniform diameter tip 16A (shown between positions C and D in FIG. 1A)for coupling, at an array interface 18A with the interface 42A of anoptical waveguide device 40A. The uniform diameter tip 16A may be usefulin certain interface applications, such as for example shown in FIGS.1D, 4 and 5. Alternatively, the coupler array 10A may be fabricatedwithout the tip 16A (or have the tip 16A removed after fabrication),such that coupling with the optical device interface 42A, occurs at acoupler array 10A interface at position C of FIG. 1A.

In an alternative embodiment, if the optical device 40A comprises adouble-clad fiber, when the small end of the coupler array 10A iscoupled (for example, fusion spliced) to the optical device interface42A, at least a portion of the common housing structure 14A proximal tothe splice position (such as at least a portion of the tip 16A), may becoated with a low index medium (not shown), extending over the spliceposition and up to the double-clad fiber optical device 40A outercladding (and optionally extending over a portion of the double-cladfiber optical device 40A outer cladding that is proximal to the spliceposition).

Referring now to FIG. 1B, a second example embodiment of the opticalfiber coupler array, is shown as a coupler array 10B. The coupler array10B comprises a common housing structure 14B, at least one VC waveguide,shown in FIG. 1B by way of example, as a single VC waveguide 30B, and atleast one Non-VC waveguide, shown in FIG. 1B by way of example, as asingle Non-VC waveguide 32B, disposed in parallel proximity to the VCwaveguide 30B, where a portion of the optical coupler array 10B, hasbeen configured to comprise a larger channel-to-channel spacing valueS2′ at its small end, than the corresponding channel-to-channel spacingvalue S2 at the small end of the optical coupler array 10A, of FIG. 1A.This configuration may be readily implemented by transversely cuttingthe optical fiber array 10A at a position C′, thus producing the commonhousing structure 14B that is shorter than the common housing structure14A and resulting in a new, larger diameter array interface 18B, havingthe larger channel-to-channel spacing value S2′.

Referring now to FIG. 1C, a third example embodiment of the opticalfiber coupler array, is shown as a coupler array 10C. The coupler array10C comprises a plurality of VC waveguides, shown in FIG. 1C as VCwaveguides 30C-1, and 30C-2, and a plurality of Non-VC waveguides, shownin FIG. 1C as Non-VC waveguides 32C-1, 32C-2, and 32C-a, all disposedlongitudinally and asymmetrically to one another, wherein at least aportion of the plural Non-VC waveguides are of different types and/ordifferent characteristics (such as single mode or multimode orpolarization maintaining etc.)—for example, Non-VC waveguides 32C-1,32C-2 are of a different type, or comprise different characteristicsfrom the Non-VC waveguide 32C-a. Additionally, any of the VC or Non-VCwaveguides (such as, for example, the Non-VC waveguide 32C-a) canreadily extend beyond the coupler array 10C common housing structure byany desired length, and need to be spliced to an optical deviceproximally thereto.

Referring now to FIG. 1D, a fourth example embodiment of the opticalfiber coupler array that is configured for multi-core fan-in and fan-outconnectivity, and shown as a coupler array 50. The coupler array 50comprises a pair of optical fiber coupler array components (10D-1 and10D-2), with a multi-core optical fiber element 52 connected (e.g., byfusion splicing at positions 54-1 and 54-2) between the second (smallersized) ends of the two optical fiber coupler array components (10D-1,10D-2). Preferably, at least one of the VC waveguides in each of thecoupler array components (10D-1, 10D-2) is configured to increase ormaximize optical coupling to a corresponding selected core of themulti-core optical fiber element 52, while decreasing or minimizingoptical coupling to all other cores thereof.

Referring now to FIG. 2A, a fifth example embodiment of the opticalfiber coupler array, is shown as a coupler array 100A. The coupler array100A comprises a plurality of longitudinally proximal VC waveguides atleast partially embedded in a single common housing structure 104A,shown by way of example only, as plural VC waveguides 130A-1, 130A-2.Each plural VC waveguide 130A-1, 130A-2 is spliced, at a particularsplice location 132A-1, 132A-2, respectively, to a correspondingrespective elongated optical device 134A-1, 134A-2 (such as an opticalfiber), at least a portion of which extends outside the common housingstructure 104A by a predetermined length 102A, and wherein eachparticular splice location 132A-1, 132A-2 is disposed within the commonhousing structure 104A.

Referring now to FIG. 2B, a sixth example embodiment of the opticalfiber coupler array, is shown as a coupler array 100B.

The coupler array 100B comprises a plurality of longitudinally proximalVC waveguides at least partially embedded in a single common housingstructure 104B, shown by way of example only, as plural VC waveguides130B-1, 130B-2. Each plural VC waveguide 130B-1, 130B-2 is spliced, at aparticular splice location 132B-1, 132B-2, respectively, to acorresponding respective elongated optical device 134B-1, 134B-2 (suchas an optical fiber), at least a portion of which extends outside thecommon housing structure 104B by a predetermined length 102B, andwherein each particular splice location 132B-1, 132B-2 is disposed at anouter cross-sectional boundary region of the common housing structure104B.

Referring now to FIG. 2C, a seventh example embodiment of the opticalfiber coupler array, is shown as a coupler array 100C.

The coupler array 100C comprises a plurality of longitudinally proximalVC waveguides at least partially embedded in a single common housingstructure 104C, shown by way of example only, as plural VC waveguides130C-1, 130C-2. Each plural VC waveguide 130C-1, 130C-2 is spliced, at aparticular splice location 132C-1, 132C-2, respectively, to acorresponding respective elongated optical device 134C-1, 134C-2 (suchas an optical fiber), at least a portion of which extends outside thecommon housing structure 104C by a predetermined length 102C, andwherein each particular splice location 132C-1, 132C-2 is disposedoutside of the common housing structure 104C.

Referring now to FIG. 2D, an alternative embodiment of the optical fibercoupler array, is shown as a coupler array 150. The coupler array 150comprises a plurality of longitudinally proximal VC waveguides at leastpartially embedded in a single common housing structure, that isconfigured at its second end, to increase or optimize optical couplingto a free-space-based optical device 152. The free-space-based opticaldevice 152 may comprise a lens 154 followed by an additional opticaldevice component 156, which may comprise, by way of example, a MEMSmirror or volume Bragg grating. The combination of the coupler and thefree-space-based optical device 152 may be used as an optical switch orWDM device for spectral combining or splitting of light signals 160 b(representative of the light coupler array 150 output light signals 160a after they have passed through the lens 154.) In this case, one of thefibers may be used as an input and all others for an output or viceversa. In another embodiment, a free-space-based device 152 can befusion spliceable to the second coupler's end. This device may be acoreless glass element, which can serve as an end cup for power densityredaction at the glass-air interface. In another modification, thecoreless element can serve as a Talbot mirror for phase synchronizationof coupler's waveguides in a Talbot cavity geometry

Prior to describing the various embodiments shown in FIGS. 3A to 3L ingreater detail, it should be understood that whenever a “plurality” or“at least one” coupler component/element is indicated below, thespecific quantity of such coupler components/elements that may beprovided in the corresponding embodiment of the coupler array, may beselected as a matter of necessity, or design choice (for example, basedon the intended industrial application of the coupler array), withoutdeparting from the spirit of the present invention. Accordingly, in thevarious FIGS. 3A to 3L, single or individual coupler arraycomponents/elements are identified by a single reference number, whileeach plurality of the coupler component/elements is identified by areference number followed by a “(1 . . . n)” designation, with “n” beinga desired number of plural coupler elements/components (and which mayhave a different value in any particular coupler array embodimentdescribed below).

Also, all the waveguides VC and Non-VC are shown with a circularcross-section of the inner and outer core and cladding only by example.Other shapes of the cross-sections of the inner and outer core andcladding (for example, hexagonal, rectangular or squared) may beutilized without departure from the current invention. The specificchoice of shape is based on various requirements, such as channel shapeof the optical device, channel positional geometry (for example,hexagonal, rectangular or square lattice), or axial polarizationalignment mode.

Similarly, unless otherwise indicated below, as long as variousrelationships set forth below (for example, the relative volumerelationship set forth below with respect to optical coupler arrays 200Cand 200D of FIGS. 3C and 3D, respectively, and the feature, set forthbelow in connection with the coupler array 200H of FIG. 3H, that the PMVC waveguide 204H is positioned longitudinally off-centered transverselyfrom the coupler array 200H central longitudinal axis), are adhered to,the sizes, relative sizes, relative positions and choices of compositionmaterials, are not limited to the example sizes, relative sizes,relative positions and choices of composition materials, indicated belowin connection with the detailed descriptions of the coupler arrayembodiments of FIGS. 3A to 3L, but rather they may be selected by oneskilled in the art as a matter of convenience or design choice, withoutdeparting from the spirit of the present invention.

Finally, it should be noted that each of the various single commonhousing structure components 202A to 202L, of the various coupler arrays200A to 200L of FIGS. 3A to 3L, respectively, may be composed of amedium having the refractive index N-4 value in accordance with anapplicable one of the above-described relationships with the values ofother coupler array component refractive indices N-1, N-2, and N-3, andhaving properties and characteristics selected from the variouscontemplated example medium composition parameters described above inconnection with medium 28A of FIG. 1A.

Referring now to FIG. 3A, a first alternative embodiment of the opticalfiber coupler array embodiments of FIGS. 1D to 2D, is shown as a couplerarray 200A in which all waveguides are VC waveguides. The coupler array200A comprises a single common housing 202A, and plurality of VCwaveguides 204A-(1 . . . n), with n being equal to 19 by way of exampleonly, disposed centrally along the central longitudinal axis of thehousing 202A. The coupler array 200A may also comprise an optional atleast one fiducial element 210A, operable to provide one or more usefulproperties to the coupler array, including, but not limited to:

-   -   enabling visual identification (at at least one of the coupler        array's ends) of the coupler array waveguide arrangement; and    -   facilitating passive alignment of at least one of the coupler        array ends to at least one optical device.

Furthermore, when deployed in optical coupler array embodiments thatcomprise at least one polarization maintaining VC waveguide (such as theoptical coupler array embodiments described below in connection withFIGS. 3H-3L), a fiducial element is further operable to:

-   -   enable visual identification of the optical coupler array's        particular polarization axes alignment mode (such as described        below in connection with FIGS. 3H-3L); and    -   serve as a geometrically positioned reference point for        alignment thereto, of one or more polarization axis of PM        waveguides in a particular optical coupler array.

The fiducial element 210A may comprise any of the various types offiducial elements known in the art, selected as a matter of designchoice or convenience without departing from the spirit of theinvention—for example, it may be a dedicated elongated elementpositioned longitudinally within the common housing structure 202A inone of various cross-sectional positions (such as positions X or Y,shown in FIG. 3A. Alternatively, the fiducial element 210A may comprisea dedicated channel not used for non-fiducial purposes, for example,replacing one of the waveguides 204A-(1 . . . n), shown by way ofexample only at position Z in FIG. 3A.

Referring now to FIG. 3B, a first alternative embodiment of the opticalfiber coupler array 10A of FIG. 1A, above, is shown as a coupler array200B, that comprises a single housing structure 202B, and at least oneVC waveguide, shown in FIG. 3B by way of example as a VC waveguide 204B,and a plurality of Non-VC waveguides 206B-(1 . . . n), with n beingequal to 18 by way of example only. The VC waveguide 204B is positionedalong a central longitudinal axis of the common housing structure 202B,and circumferentially and symmetrically surrounded by proximal parallelplural Non-VC waveguides 206B-(1 . . . n).

Referring now to FIG. 3C, a first alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200C that comprises a single housing structure 202C, a VC waveguide204C, and a plurality of Non-VC waveguides 206C-(1 . . . n), with nbeing equal to 18 by way of example only. The VC waveguide 204C ispositioned along a central longitudinal axis of the common housingstructure 202C, and circumferentially and symmetrically surrounded byproximal parallel plural Non-VC waveguides 206C-(1 . . . n). The couplerarray 200C is configured such that a volume of the common housingstructure 202C medium, surrounding the sections of all of the waveguidesembedded therein (i.e., the VC waveguide 204C and the plural Non-VCwaveguides 206C-(1 . . . n)), exceeds a total volume of the inner andouter cores of the section of the VC waveguide 204C that is embeddedwithin the single common housing structure 202C.

Referring now to FIG. 3D, a first alternative embodiment of the opticalfiber coupler array 200C of FIG. 3C, above, is shown as a coupler array200D that comprises a single housing structure 202D, a plurality of VCwaveguides 204D-(1 . . . N), with N being equal to 7 by way of exampleonly, and a plurality of Non-VC waveguides 206D-(1 . . . n), with nbeing equal to 12 by way of example only. The plural VC waveguides204D-(1 . . . N) are positioned along a central longitudinal axis of thecommon housing structure 202D, and circumferentially and symmetricallysurrounded by proximal parallel plural Non-VC waveguides 206D-(1 . . .n). The coupler array 200D is configured such that a volume of thecommon housing structure 202D medium, surrounding the sections of all ofthe waveguides embedded therein (e.g., the plural VC waveguides 204D-(1. . . N), and the plural Non-VC waveguides 206D-(1 . . . n)), exceeds atotal volume of the inner and outer cores of the section of the pluralVC waveguides 204D-(1 . . . N) that are embedded within the singlecommon housing structure 202D.

Referring now to FIG. 3E, a first alternative embodiment of the opticalfiber coupler array 200D of FIG. 3D, above, is shown as a coupler array200E, that comprises a single housing structure 202E, a plurality of VCwaveguides 204E-(1 . . . N), with N being equal to 6 by way of exampleonly, a plurality of Non-VC waveguides 206E-(1 . . . n), with n beingequal to 12 by way of example only, and a separate single Non-VCwaveguide 206E′. The Non-VC waveguide 206E′, is preferably operable toprovide optical pumping functionality therethrough, and is positionedalong a central longitudinal axis of the common housing structure 202Eand circumferentially and symmetrically surrounded by proximal parallelplural VC waveguides 204E-(1 . . . N), that are in turncircumferentially and symmetrically surrounded by proximal parallelplural Non-VC waveguides 206E-(1 . . . n).

Referring now to FIG. 3F, a second alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200F, that comprises a single housing structure 202F, a plurality of VCwaveguides 204F-(1 . . . N), with N being equal to 6 by way of exampleonly, a separate single VC waveguide 204F′, and a plurality of Non-VCwaveguides 206F-(1 . . . n), with n being equal to 12 by way of exampleonly, that preferably each comprise enlarged inner cores of sufficientdiameter to increase or optimize optical coupling to different types ofoptical pump channels of various optical devices, to which the couplerarray 200F may be advantageously coupled. The VC waveguide 204F′, ispositioned along a central longitudinal axis of the common housingstructure 202F, and circumferentially and symmetrically surrounded byproximal parallel plural VC waveguides 204F-(1 . . . N), that are inturn circumferentially and symmetrically surrounded by proximal parallelplural Non-VC waveguides 206F-(1 . . . n).

Referring now to FIG. 3G, a third alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200G, that comprises a single housing structure 202G, and at least oneVC waveguide, shown in FIG. 3G by way of example as a VC waveguide 204G,and a plurality of Non-VC waveguides 206G-(1 . . . n), with n beingequal to 18 by way of example only. The VC waveguide 204G is positionedas a side-channel, off-set from the central longitudinal axis of thesingle common housing structure 202G, such that optical fiber couplerarray 200G may be readily used as a fiber optical amplifier and or alaser, when spliced to a double-clad optical fiber (not shown) having anon-concentric core for improved optical pumping efficiency. It shouldbe noted that because a double-clad fiber is a fiber in which both thecore and the inner cladding have light guiding properties, most opticalfiber types, such as SM, MM, LMA, or MC (multi-core), whetherpolarization maintaining or not, and even standard (e.g., conventional)single mode optical fibers, can be converted into a double-clad fiber bycoating (or recoating) the fiber with a low index medium (forming theouter cladding).

Optionally, when the second end of the coupler array 200G is spliced toa double-clad fiber (not shown), at least a portion of the commonhousing structure 202G proximal to the splice point with the double-cladfiber (not-shown), may be coated with a low index medium extending overthe splice point and up to the double-clad fiber's outer cladding (andoptionally extending over a portion of the outer cladding that isproximal to the splice point).

Referring now to FIGS. 3H to 3L, in various alternative exampleembodiments of the optical coupler, at least one of the VC waveguidesutilized therein, and, in certain embodiments, optionally at least oneof the Non-VC waveguides, may comprise a polarization maintaining (PM)property. By way of example, the PM property of a VC waveguide mayresult from a pair of longitudinal stress rods disposed within the VCwaveguide outside of its inner core and either inside, or outside, ofthe outer core (or through other stress elements), or the PM propertymay result from a noncircular inner or outer core shape, or from otherPM-inducing optical fiber configurations (such as in bow-tie orelliptically clad PM fibers). In various embodiments of the opticalfiber in which at least one PM waveguide (VC and/or Non-VC) is utilized,an axial alignment of the PM waveguides (or waveguide), in accordancewith a particular polarization axes alignment mode may be involved.

In accordance with certain embodiments, a polarization axes alignmentmode may comprise, but is not limited to, at least one of the following:

-   -   axial alignment of a PM waveguide's polarization axis to the        polarization axes of other PM waveguides in the optical coupler;        when a PM waveguide is positioned off-center: axial alignment of        a PM waveguide's polarization axis to its transverse        cross-sectional (geometric) position within the optical coupler;    -   when the single common housing structure of the optical coupler        comprises a non-circular geometric shape (such as shown by way        of example in FIG. 3L): axial alignment of a PM waveguide's        polarization axis to a geometric feature of the common housing        structure outer shape;    -   in optical coupler embodiments comprising one or more waveguide        arrangement indicators, described below, in connection with        FIGS. 3J-3L: axial alignment of a PM waveguide's polarization        axis to at least one geometric characteristic thereof;    -   in optical coupler embodiments comprising at least one fiducial        element 210A, as described above in connection with FIG. 3A:        axial alignment of a PM waveguide's polarization axis to a        geometric position of the at least one fiducial element 210A;

The selection of a specific type of polarization axes alignment mode forthe various embodiments of the optical coupler is preferably governed byat least one axes alignment criterion, which may include, but which isnot limited to: alignment of PM waveguides' polarization axes in ageometric arrangement that increases or maximizes PM properties thereof;and/or satisfying at least one requirement of one or more intendedindustrial application for the coupler array.

Referring now to FIG. 3H, a first alternative embodiment of the opticalfiber coupler array 200G of FIG. 3G, above, is shown as a coupler array200H, that comprises a single housing structure 202H, and at least oneVC waveguide, shown in FIG. 3H by way of example as a PM VC waveguide204H having polarization maintaining properties, and a plurality ofNon-VC waveguides 206H-(1 . . . n), with n being equal to 18 by way ofexample only. The PM VC waveguide 204H is positioned as a side-channel,off-set from the central longitudinal axis of the single common housingstructure 202H, and comprises a polarization axis that is aligned, byway of example, with respect to the transverse off-center location ofthe PM VC waveguide 204H.

Referring now to FIG. 3I, a fourth alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200I, that comprises a single housing structure 202I, and at least oneVC waveguide, shown in FIG. 3I by way of example as a PM VC waveguide204I having polarization maintaining properties, and a plurality of PMNon-VC waveguides 206I-(1 . . . n), with n being equal to 18 by way ofexample only, each also having polarization maintaining properties. ThePM VC waveguide 204I is positioned along a central longitudinal axis ofthe common housing structure 202I, and circumferentially andsymmetrically surrounded by proximal parallel plural PM Non-VCwaveguides 206I-(1 . . . n). By way of example, the coupler array 200Icomprises a polarization axes alignment mode in which the polarizationaxes of each of the PM VC waveguide 204I and of the plural PM Non-VCwaveguides 206I-(1 . . . n) are aligned to one another. The PMproperties of the PM VC waveguide 204I and of the plural PM Non-VCwaveguides 206I-(1 . . . n) are shown, by way of example only, as beinginduced by rod stress members (and which may readily and alternately beinduced by various other stress, or equivalent designs)).

Referring now to FIG. 3J, a first alternative embodiment of the opticalfiber coupler array 200I of FIG. 3I, above, is shown as a coupler array200J, that comprises a single housing structure 202J, and at least oneVC waveguide, shown in FIG. 3J by way of example as a PM VC waveguide204J having polarization maintaining properties, and a plurality of PMNon-VC waveguides 206J-(1 . . . n), with n being equal to 18 by way ofexample only, each also having polarization maintaining properties. ThePM VC waveguide 204J is positioned along a central longitudinal axis ofthe common housing structure 202J, and circumferentially andsymmetrically surrounded by proximal parallel plural PM Non-VCwaveguides 206J-(1 . . . n). The PM properties of the PM VC waveguide204J and of the plural PM Non-VC waveguides 206J-(1 . . . n) are shown,by way of example only, as resulting only from a non-circularcross-sectional shape (shown by way of example only as being at least inpart elliptical), of each plural PM Non-VC waveguide 206J-(1 . . . n)core (and from a non-circular cross-sectional shape of the outer core ofthe PM VC waveguide 204J).

The coupler array 200J optionally comprises at least one waveguidearrangement indication element 208J, positioned on an outer region ofthe common housing structure 202J, that is representative of theparticular cross-sectional geometric arrangement of the optical couplerarray 200J waveguides (i.e., of the PM VC waveguide 204J and of theplural PM Non-VC waveguides 206J-(1 . . . n)), such that a particularcross-sectional geometric waveguide arrangement may be readilyidentified from at least one of a visual and physical inspection of thecommon coupler housing structure 202J that is sufficient to examine thewaveguide arrangement indication element 208J. Preferably, the waveguidearrangement indication element 208J may be configured to be furtheroperable to facilitate passive alignment of a second end of the opticalcoupler array 200J to at least one optical device (not shown).

The waveguide arrangement indication element 208J, may comprise, but isnot limited to, one or more of the following, applied to the commonhousing structure 202J outer surface: a color marking, and/or a physicalindicia (such as an groove or other modification of the common housingstructure 202J outer surface, or an element or other member positionedthereon). Alternatively, the waveguide arrangement indication element208J may actually comprise a specific modification to, or definition of,the cross-sectional geometric shape of the common housing structure 202J(for example, such as a hexagonal shape of a common housing structure202L of FIG. 3L, below, or another geometric shape).

By way of example, the coupler array 200J may comprise a polarizationaxes alignment mode in which the polarization axes of each of the PM VCwaveguide 204J and of the plural PM Non-VC waveguides 206J-(1 . . . n)are aligned to one another, or to the waveguide arrangement indicationelement 208J.

Referring now to FIG. 3K, a fifth alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200K, that comprises a single housing structure 202K, and at least oneVC waveguide, shown in FIG. 3K by way of example as a PM VC waveguide204K having polarization maintaining properties, and a plurality ofNon-VC waveguides 206K-(1 . . . n), with n being equal to 18 by way ofexample only. The PM VC waveguide 204K is positioned along a centrallongitudinal axis of the common housing structure 202K, andcircumferentially and symmetrically surrounded by proximal parallelplural PM Non-VC waveguides 206K-(1 . . . n). The PM properties of thePM VC waveguide 204K are shown, by way of example only, as being inducedby rod stress members (and which may readily and alternately be inducedby various other stress, or equivalent approaches)). The coupler array200K, may optionally comprise a plurality of waveguide arrangementindication elements—shown by way of example only, as waveguidearrangement indication elements 208K-a and 208K-b, which may each be ofthe same, or of a different type, as described above, in connection withthe waveguide arrangement indication element 208J of FIG. 3J.

Referring now to FIG. 3L, a second alternative embodiment of the opticalfiber coupler array 200I of FIG. 3I, above, is shown as a coupler array200L, that comprises a single housing structure 202L comprising a crosssection having a non-circular geometric shape (shown by way of exampleas a hexagon), and at least one VC waveguide, shown in FIG. 3L by way ofexample as a PM VC waveguide 204L having polarization maintainingproperties, and a plurality of PM Non-VC waveguides 206L-(1 . . . n),with n being equal to 18 by way of example only, each also havingpolarization maintaining properties. The PM VC waveguide 204L ispositioned along a central longitudinal axis of the common housingstructure 202L, and circumferentially and symmetrically surrounded byproximal parallel plural PM Non-VC waveguides 206L-(1 . . . n).

By way of example, the coupler array 200L comprises a polarization axesalignment mode in which the polarization axes of each of the PM VCwaveguide 204L and of the plural PM Non-VC waveguides 206L-(1 . . . n)are aligned to one another, and to the common housing structure 202Lcross-sectional geometric shape. The PM properties of the PM VCwaveguide 204L and of the plural PM Non-VC waveguides 206L-(1 . . . n)are shown, by way of example only, as being induced by rod stressmembers (and which may readily and alternately be induced by variousother stress, or equivalent designs)). The coupler array 200K, mayoptionally comprise a waveguide arrangement indication element 208L-awhich may comprise any of the configurations described above, inconnection with the waveguide arrangement indication element 208J ofFIG. 3J.

Referring now to FIG. 4, a second end 302 (i.e. “tip”) of the opticalfiber coupler array is shown, by way of example, as being in the processof connecting to plural vertical coupling elements 306 of an opticaldevice 304 in a proximal open air optical coupling alignmentconfiguration, that may be readily shifted into a butt-coupledconfiguration through full physical contact of the optical fiber couplerarray second end 302 and the vertical coupling elements 306.

Referring now to FIG. 5 a second end 322 (i.e. “tip”) of the opticalfiber coupler array is shown, by way of example, as being in the processof connecting to plural edge coupling elements 326 of an optical device324 in a butt-coupled configuration, that may be readily shifted intoone of several alternative coupling configuration, including a proximalopen air optical coupling alignment configuration, and or an angledalignment coupling configuration.

In at least one alternative embodiment, the optical coupler array (i.e.,such as optical coupler arrays 200D to 200L of FIGS. 3C to 3L) may bereadily configured to pump optical fiber lasers, and/or optical fiberamplifiers (or equivalent devices). In a preferred embodiment thereof, apumping-enabled coupler array comprises a central channel (i.e.,waveguide), configured to transmit a signal (i.e., serving as a “signalchannel”) which will thereafter be amplified or utilized to generatelasing, and further comprises at least one additional channel (i.e.,waveguide), configured to provide optical pumping functionality (i.e.,each serving as a “pump channel”). In various example alternativeembodiments thereof, the pumping-enabled coupler array may comprise thefollowing in any desired combination thereof:

-   -   at least one of the following signal channels: a single mode        signal channel configured for increased or optimum coupling to a        single mode amplifying fiber at at least one predetermined        signal or lasing wavelength, a multimode signal channel        configured for increased or optimum coupling to a multimode        amplifying fiber at at least one predetermined signal or lasing        wavelength, and    -   at least one of the following pumping channels: a single mode        pumping channel configured for increased or optimum coupling to        a single mode pump source at at least one predetermined pumping        wavelength, a multimode pumping channel configured for increased        or optimum coupling to a multimode pump source at at least one        predetermined pumping wavelength.

Optionally, to increase or maximize pumping efficiency, thepumping-enabled coupler array may be configured to selectively utilizeless than all the available pumping channels. It should also be notedthat, as a matter of design choice, and without departing from thespirit of the invention, the pumping-enabled coupler array may beconfigured to comprise:

-   -   a. At least one signal channel, each disposed in a predetermined        desired position in the coupler array structure;    -   b. At least one pumping channel, each disposed in a        predetermined desired position in the coupler array structure;        and    -   c. Optionally—at least one additional waveguide for at least one        additional purpose other than signal transmission or pumping        (e.g., such as a fiducial marker for alignment, for fault        detection, for data transmission, etc.)

Advantageously, the pump channels could be positioned in any transverseposition within the coupler, including along the central longitudinalaxis. The pump channels may also comprise, but are not limited to, atleast one of any of the following optical fiber types: SM, MM, LMA, orVC waveguides. Optionally, any of the optical fiber(s) being utilized asan optical pump channel (regardless of the fiber type) in the couplermay comprise polarization maintaining properties.

In yet another example embodiment, the pumping-enabled coupler array maybe configured to be optimized for coupling to a double-clad fiber—inthis case, the signal channel of the coupler array would be configuredor optimized for coupling to the signal channel of the double-cladfiber, while each of the at least one pumping channels would beconfigured or optimized to couple to the inner cladding of thedouble-clad fiber.

In essence, the optical coupler arrays, shown by way of example invarious embodiments, may also be readily implemented as high density,multi-channel, optical input/output (I/O) for fiber-to-chip andfiber-to-optical waveguides. The optical fiber couplers may readilycomprise at least the following features:

-   -   Dramatically reduced channel spacing and device footprint (as        compared to previously known solutions)    -   Scalable channel count    -   All-glass optical path    -   Readily butt-coupled or spliced at their high density face        without the need of a lens, air gap, or a beam spreading medium    -   May be fabricated through a semi-automated production process    -   Broad range of customizable parameters: wavelength, mode field        size, channel spacing, array configuration, fiber type.

The optical fiber couplers may be advantageously utilized for at leastthe following applications, as a matter of design choice or convenience,without departing from the spirit of the invention:

-   -   Coupling to waveguides:        -   PIC or PCB-based (single-mode or multimode)        -   Multicore fibers        -   Chip edge (1D) or chip face (2D) coupling        -   NA optimized for the application, factoring in:            -   Packaging alignment needs            -   Chip processing needs/waveguide up-tapering        -   Polarization maintaining properties may be readily            configured    -   Coupling to chip-based devices: e.g. VCSELs, photodiodes,        vertically coupled gratings    -   Laser diode coupling    -   High density equipment Input/Output (I/O)

Accordingly, when implemented, the various example embodiments of theoptical fiber couplers comprise at least the following advantages, ascompared to currently available competitive solutions:

-   -   Unprecedented density    -   Low-loss coupling (≤0.5 dB)    -   Operational stability    -   Form factor support    -   Broad spectral range    -   Matching NA    -   Scalable channel count    -   Polarization maintenance

Referring now to FIG. 7, at least one example embodiment of a flexibleoptical coupler array is shown as a flexible pitch reducing opticalfiber array (PROFA) coupler 450. Although various features of theexample PROFA coupler may be described with respect to FIG. 7, anyfeature described above can be implemented in any combination with aflexible PROFA coupler. For example, any of the features described withrespect to FIGS. 1A-5 may be utilized in a flexible PROFA coupler.Further, any feature described with respect to FIGS. 1A-5 may becombined with any feature described with respect to FIG. 7.

With continued reference to FIG. 7, the example flexible PROFA coupler450 shown in FIG. 7 can be configured for use in applicationswhereinterconnections with low crosstalk and sufficient flexibility toaccommodate low profile packaging are desired. The vanishing coreapproach, described herein and in U.S. Patent Application PublicationNo. 2013/0216184, entitled “CONFIGURABLE PITCH REDUCING OPTICAL FIBERARRAY”, which is hereby incorporated herein in its entirety, allows forthe creation of a pitch reducing optical fiber array (PROFA)coupler/interconnect operable to optically couple, for example, aplurality of optical fibers to an optical device (e.g., a PIC), whichcan be butt-coupled to an array of vertical grating couplers (VGCs). Ifthe cross sectional structure of the coupler 450 has an additional layerof refractive index, N-2A, even lower than N2, as described herein andin U.S. Patent Application Publication No. 2013/0216184, the vanishingcore approach can be utilized once more to reduce the outside diameterfurther without substantially compromising the channel crosstalk. Thisfurther reduction can advantageously provide certain embodiments with aflexible region which has a reduced cross section between a first andsecond end.

In some preferred embodiments, the difference (N-2A minus N-3) is largerthan the differences (N-2 minus N-2A) or (N-1 minus N-2), resulting in ahigh NA, bend insensitive waveguide, when the light is guided by theadditional layer having refractive index N-2A. Also, in some preferredembodiments, after the outside diameter of the coupler 450 is reducedalong a longitudinal length from one end to form the flexible region,the outer diameter can then be expanded along the longitudinal lengthtoward the second end, resulting in a lower NA waveguide with largercoupling surface area at the second end.

For example, as illustrated in FIG. 7, certain embodiments of an opticalcoupler array 450 can comprise an elongated optical element 1000 havinga first end 1010, a second end 1020, and a flexible portion 1050therebetween. The optical element 1000 can include a coupler housingstructure 1060 and a plurality of longitudinal waveguides 1100 embeddedin the housing structure 1060. The waveguides 1100 can be arranged withrespect to one another in a cross-sectional geometric waveguidearrangement. In FIG. 7, the example cross-sectional geometric waveguidearrangements of the waveguides 1100 for the first end 1010, the secondend 1020, and at a location within the flexible portion 1050 are shown.The cross-sectional geometric waveguide arrangement of the waveguides1100 for an intermediate location 1040 between the first end 1010 andthe flexible portion 1050 is also shown. As illustrated by the shadedregions within the cross sections and as will be described herein, lightcan be guided through the optical element 1000 from the first end 1010to the second end 1020 through the flexible portion 1050. As also shownin FIG. 7, this can result in a structure, which maintains all channelsdiscretely with sufficiently low crosstalk, while providing enoughflexibility (e.g., with the flexible portion 1050) to accommodate lowprofile packaging.

The level of crosstalk and/or flexibility can depend on the applicationof the array. For example, in some embodiments, a low crosstalk can beconsidered within a range from −45 dB to −35 dB, while in otherembodiments, a low crosstalk can be considered within a range from −15dB to −5 dB. Accordingly, the level of crosstalk is not particularlylimited. In some embodiments, the crosstalk can be less than or equal to−55 dB, −50 dB, −45 dB, −40 dB, −35 dB, −30 dB, −25 dB, −20 dB, −15 dB,−10 dB, 0 dB, or any values therebetween (e.g., less than or equal to−37 dB, −27 dB, −17 dB, −5 dB, etc.) In some embodiments, the crosstalkcan be within a range from −50 dB to −40 dB, from −40 dB to −30 dB, from−30 dB to −20 dB, from −20 dB to −10 dB, from −10 dB to 0 dB, from −45dB to −35 dB, from −35 dB to −25 dB, from −25 dB to −15 dB, from −15 dBto −5 dB, from −10 dB to 0 dB, any combinations of these ranges, or anyranges formed from any values from −55 dB to 0 dB (e.g., from −52 dB to−37 dB, from −48 dB to −32 dB, etc.).

The flexibility can also depend on the application of the array. Forexample, in some embodiments, good flexibility of the flexible portion1050 can comprise bending of at least 90 degrees, while in otherembodiments, a bending of at least 50 degrees may be acceptable.Accordingly, the flexibility is not particularly limited. In someembodiments, the flexibility can be at least 45 degrees, 50 degrees, 55degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 90degrees, 100 degrees, 110 degrees, 120 degrees, or at least any valuetherebetween. In some embodiments, the flexible portion 1050 can bend ina range formed by any of these values, e.g., from 45 to 55 degrees, from50 to 60 degrees, from 60 to 70 degrees, from 70 to 80 degrees, from 80to 90 degrees, from 90 to 100 degrees, from 100 to 110 degrees, from 110to 120 degrees, or any combinations of these ranges, or any rangesformed by any values within these ranges (e.g., from 50 to 65 degrees,from 50 to 85 degrees, from 65 to 90 degrees, etc.) In otherembodiments, the flexible portion 1050 can bend more or less than thesevalues. Bending can typically be associated with light scattering.However, various embodiments can be configured to bend as describedherein (e.g., in one of the ranges described above) and achieverelatively low crosstalk as described herein (e.g., in one of the rangesdescribed above).

In various applications, the flexible portion 1050 might not bend inuse, however the flexibility can be desired for decoupling the first1010 or second 1020 end from other parts of the coupler array 450. Forexample, the flexible portion 1050 of the flexible PROFA coupler 450 canprovide mechanical isolation of the first end 1010 (e.g., a PROFA-PICinterface) from the rest of the PROFA, which results in increasedstability with respect to environmental fluctuations, includingtemperature variations and mechanical shock and vibration.

In the example shown in FIG. 7, the coupler array 450 can be operable tooptically couple with a plurality of optical fibers 2000 and/or with anoptical device 3000. The optical fibers 2000 and optical device 3000 caninclude any of those described herein. The coupler array 450 can couplewith the optical fibers 2000 via the plurality of waveguides 1100 at thefirst end 1010. In addition, the coupler array 450 can couple with theoptical device 3000 via the plurality of waveguides 1100 at the secondend 1020. As described herein, the plurality of waveguides 1100 caninclude at least one VC waveguide 1101. FIG. 7 illustrates all of thewaveguides 1100 as VC waveguides. However, one or more Non-VC waveguidesmay also be used. In addition, FIG. 7 illustrates 7 VC waveguides, yetany number of VC and/or Non-VC waveguides can be used.

As also shown in the cross sections, each of the waveguides 1100 can bedisposed at an individual corresponding cross-sectional geometricposition, relative to other waveguides of the plurality of waveguides1100. Although FIG. 7 shows a waveguide surrounded by 6 otherwaveguides, the cross-sectional geometric waveguide arrangement is notlimited and can include any arrangement known in the art or yet to bedeveloped including any of those shown in FIGS. 3A-3L.

As described herein, the VC waveguide 1101 can include an inner core(e.g., an inner vanishing core) 1110, an outer core 1120, and an outercladding 1130 with refractive indices N-1, N-2, and N-3 respectively. Asshown in FIG. 7, the VC waveguide 1101 can also include a secondaryouter core 1122 (e.g., between the outer core 1120 and the outercladding 1130) having refractive index N-2A. As the outer core 1120 canlongitudinally surround the inner core 1110, the secondary outer core1122 can longitudinally surround the outer core 1120 with the outercladding 1130 longitudinally surrounding the secondary outer core 1122.In various embodiments, the relationship between the refractive indicesof the inner core 1110, outer core 1120, secondary outer core 1122, andouter cladding 1130 can advantageously be N-1>N-2>N2-A>N-3. With such arelationship, each surrounding layer can serve as an effective claddingto the layers within it (e.g., the outer core 1120 can serve as aneffective cladding to the inner core 1110, and the secondary outer core1122 can serve as an effective cladding to the outer core 1120). Hence,the use of the secondary outer core 1122 can provide an additional setof core and cladding.

By including the secondary outer core 1122 with a refractive index N-2A,certain embodiments can achieve a higher NA (e.g., compared to withoutthe secondary outer core 1122). In various embodiments, the difference(N-2A minus N-3) can be larger than the differences (N-2 minus N-2A) or(N-1 minus N-2) to result in a relatively high NA. Increasing NA canreduce the MFD, allowing for the channels (e.g., waveguides 1100) to becloser to each other (e.g., closer spacing between the waveguides 1100)without compromising crosstalk. Accordingly, the coupler array 450 canbe reduced further in cross section (e.g., compared to without thesecondary outer core 1122) to provide a reduced region when light isguided by the secondary outer core 1122. By providing a reduced regionbetween the first end 1010 and the second end 1020, certain embodimentscan include a flexible portion 1050 which can be more flexible than theregions proximal to the first end 1010 and the second end 1020.

For example, the inner core 1110 size, the outer core 1120 size, and thespacing between the waveguides 1100 can reduce (e.g., simultaneously andgradually in some instances) along the optical element 1000 from thefirst end 1010 to the intermediate location 1040 such that at theintermediate location 1040, the inner core 1110 size is insufficient toguide light therethrough and the outer core 1120 size is sufficient toguide at least one optical mode. In certain embodiments, each waveguide1100 can have a capacity for at least one optical mode (e.g., singlemode or multi-mode). For example, at the first end 1010, the VCwaveguide 1101 can support a number of spatial modes (M1) within theinner core 1110. At the intermediate location 1040, in variousembodiments, the inner core 1110 may no longer be able to support allthe M1 modes (e.g., cannot support light propagation). However, in somesuch embodiments, at the intermediate location 1040, the outer core 1120can be able to support all the M1 modes (and in some cases, able tosupport additional modes). In this example, light traveling within theinner core 1110 from the first end 1010 to the intermediate location1040 can escape from the inner core 1110 into the outer core 1120 suchthat light can propagate within both the inner core 1110 and outer core1120.

In addition, the outer core 1120 size, the secondary outer core 1122size, and the spacing between the waveguides 1100 can reduce (e.g.,simultaneously and gradually in some instances) along said opticalelement 1000, for example, from the intermediate location 1040 to theflexible portion 1050 such that at the flexible portion 1050, the outercore 1120 size is insufficient to guide light therethrough and thesecondary outer core 1122 size is sufficient to guide at least oneoptical mode therethrough. In certain embodiments, at the intermediatelocation 1040, the VC waveguide 1101 can support all the M1 modes withinthe outer core 1120. At the flexible portion 1050, in variousembodiments, the outer core 1120 may be no longer able to support allthe M1 modes (e.g., cannot support light propagation). However, in somesuch embodiments, at the flexible portion 1050, the secondary outer core1122 can be able to support all the M1 modes (and in some cases, able tosupport additional modes). In this example, light traveling within theouter core 1120 from the intermediate location 1040 to the flexibleportion 1050 can escape from the outer core 1120 into the secondaryouter core 1122 such that light can propagate within the inner core1110, the outer core 1120, and secondary outer core 1122.

Furthermore, the outer core 1120 size, the secondary outer core 1122size, and the spacing between the waveguides 1100 can expand (e.g.,simultaneously and gradually in some instances) along the opticalelement 1000 from the flexible portion 1050 to the second end 1020 suchthat at the second end 1020, the secondary outer core 1122 size isinsufficient to guide light therethrough and the outer core 1120 size issufficient to guide at least one optical mode therethrough. In certainembodiments, at the second end 1020, in various embodiments, thesecondary outer core 1122 may no longer be able to support all the M1modes (e.g., cannot support light propagation). However, in some suchembodiments, at the second end 1020, the outer core 1120 can be able tosupport all the M1 modes (and in some cases, able to support additionalmodes). In this example, light traveling within the secondary outer core1122 from the flexible portion 1050 to the second end 1020 can returnand propagate only within the inner core 1110 and the outer core 1120.

It would be appreciated that light travelling from the second end 1020to the first end 1010 can behave in the reverse manner. For example, theouter core 1120 size, the secondary outer core 1122 size, and spacingbetween the waveguides 1100 can reduce (e.g., simultaneously andgradually in some instances) along the optical element 1000 from thesecond end 1020 to the flexible portion 1050 such that at the flexibleportion 1050, the outer core 1120 size is insufficient to guide lighttherethrough and the secondary outer core 1122 size is sufficient toguide at least one optical mode therethrough.

The reduction in cross-sectional core and cladding sizes canadvantageously provide rigidity and flexibility in a coupler array 450.Since optical fibers 2000 and/or an optical device 3000 can be fused tothe ends 1010, 1020 of the coupler array 450, rigidity at the first 1010and second 1020 ends can be desirable. However, it can also be desirablefor coupler arrays to be flexible so that they can bend to connect withlow profile integrated circuits. In certain embodiments, the flexibleportion 1050 between the first 1010 and second 1020 ends can allow thefirst 1010 and second 1020 ends to be relatively rigid, while providingthe flexible portion 1050 therebetween. The flexible portion can extendover a length of the optical element 1000 and can mechanically isolatethe first 1010 and second 1020 ends. For example, the flexible portion1050 can mechanically isolate the first end 1010 from a region betweenthe flexible portion 1050 and the second end 1020. As another example,the flexible portion 1050 can mechanically isolate the second end 1020from a region between the first end 1010 and the flexible portion 1050.Such mechanical isolation can provide stability to the first 1010 andsecond 1020 ends, e.g., with respect to environmental fluctuations,including temperature variations and mechanical shock and vibration. Thelength of the flexible portion 1050 is not particularly limited and candepend on the application. In some examples, the length can be in arange from 2 to 7 mm, from 3 to 8 mm, from 5 to 10 mm, from 7 to 12 mm,from 8 to 15 mm, any combination of these ranges, or any range formedfrom any values from 2 to 20 mm (e.g., 3 to 13 mm, 4 to 14 mm, 5 to 17mm, etc.). In other examples, the length of the flexible portion 1050can be shorter or longer.

At the same time, the flexible portion 1050 can provide flexibility. Inmany instances, the flexible portion 1050 can have a substantiallysimilar cross-sectional size (e.g., the cross-sectional size of thewaveguides 1100) extending over the length of the flexible portion 1050.In certain embodiments, the cross-section size at the flexible portion1050 can comprise a smaller cross-sectional size than thecross-sectional size at the first 1010 and second 1020 ends. Having asmaller cross-sectional size, this flexible portion 1050 can be moreflexible than a region proximal to the first 1010 and second 1020 ends.The smaller cross-sectional size can result from the reduction in coreand cladding sizes. An optional etching post-process may be desirable tofurther reduce the diameter of the flexible length of the flexible PROFAcoupler 450.

In some embodiments, the flexible portion 1050 can be more flexible thana standard SMF 28 fiber. In some embodiments, the flexible portion 1050can bend at least 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65degrees, 70 degrees, 75 degrees, 80 degrees, 90 degrees, 100 degrees,110 degrees, 120 degrees, or at least any value therebetween. In someembodiments, the flexible portion 1050 can bend in a range formed by anyof these values, e.g., from 45 to 55 degrees, from 50 to 60 degrees,from 60 to 70 degrees, from 70 to 80 degrees, from 80 to 90 degrees,from 90 to 100 degrees, from 100 to 110 degrees, from 110 to 120degrees, or any combinations of these ranges, or any ranges formed byany values within these ranges (e.g., from 50 to 65 degrees, from 50 to85 degrees, from 65 to 90 degrees, etc.) In other embodiments, theflexible portion 1050 can bend more or less than these values. Asdescribed herein, in various applications, the flexible portion 1050might not bend in use, however the flexibility can be desired fordecoupling the first 1010 or second 1020 end from other parts of thecoupler array 450.

The coupler array 450 can include a coupler housing structure 1060. Forexample, the coupler housing structure 1060 can include a common singlecoupler housing structure. In certain embodiments, the coupler housingstructure 1060 can include a medium 1140 (e.g., having a refractiveindex N-4) surrounding the waveguides 1100. In some instances, N-4 isgreater than N-3. In other examples, N-4 is equal to N-3. The medium1140 can include any medium as described herein (e.g., pure-silica). Themedium can also include glass such that the coupler array 450 can be anall-glass coupler array. The waveguides 1100 can be embedded within themedium 1040 of the housing structure 1060. In some examples, a totalvolume of the medium 1140 of the coupler housing structure 1060 can begreater than a total volume of all the inner and outer cores 1110, 1120,1122 of the VC waveguides confined within the coupler housing structure1060.

In some embodiments, each waveguide can couple to the optical fibers2000 and/or optical device 3000 at a location inside, outside, or at aboundary region of the coupler housing structure 1060, e.g., as shown inFIGS. 1A to 2D. Because the optical fibers 2000 and optical device 3000can be different at each end, the first end 1010 and the second end 1020can each be configured for the optical fibers 2000 or optical device3000 with which it is coupled. For example, the MFD of the VC waveguideat the first 1010 and/or second 1020 ends can be configured (e.g., usingthe sizes of the cores) to match or substantially match the MFD of theoptical fiber 2000 or optical device 3000 with which it is coupled. Inaddition, the NA of the VC waveguide at the first 1010 and/or second1020 ends can be configured (e.g., using the refractive indices) tomatch or substantially match the NA of the optical fiber 2000 or opticaldevice 3000 with which it is coupled. The refractive indices can bemodified in any way known in the art (e.g., doping the waveguide glass)or yet to be developed. In various embodiments, as described herein, thedifference (N-1 minus N-2) can be greater than the difference (N-2 minusN-2A) such that the NA at the first end 1010 is greater than the NA atthe second end 1020. In other embodiments, the difference (N-1 minusN-2) can be less than the difference (N-2 minus N-2A) such that the NAat the first end 1010 is less than the NA at the second end 1020. In yetother embodiments, the difference (N-1 minus N-2) can be equal to (N-2minus N-2A) such that the NA at the first end 1010 is equal to the NA atthe second end 1020. The VC waveguide can include any of the fiber typesdescribed herein including but not limited to a single mode fiber, amulti-mode fiber, and/or a polarization maintaining fiber.

The core and cladding (1110, 1120, 1122, 1130) sizes (e.g., outercross-sectional diameters if circular or outer cross-sectionaldimensions if not circular) are not particularly limited. In someembodiments, the inner 1110 and/or outer 1120 core sizes can be in arange from 1 to 3 microns, from 2 to 5 microns, from 4 to 8 microns,from 5 to 10 microns, any combination of these ranges, or any rangeformed from any values from 1 to 10 microns (e.g., 2 to 8 microns, 3 to9 microns, etc.). However, the sizes can be greater or less. Forexample, the inner 1110 and/or outer 1120 core sizes can range fromsubmicrons to many microns, to tens of microns, to hundreds of micronsdepending, for example, on the wavelength and/or number of modesdesired.

In addition, the difference in the refractive indices (e.g., between N-1and N-2, between N-2 and N-2A, and/or between N-2A and N-3) is notparticularly limited. In some examples, the index difference can be in arange from 1.5×10⁻³ to 2.5×10⁻³, from 1.7×10⁻³ to 2.3×10⁻³, from1.8×10⁻³ to 2.2×10⁻³, from 1.9×10⁻³ to 2.1×10⁻³, from 1.5×10⁻³ to1.7×10⁻³, from 1.7×10⁻³ to 1.9×10⁻³, from 1.9×10⁻³ to 2.1×10⁻³, from2.1×10⁻³ to 2.3×10⁻³, from 2.3×10⁻³ to 2.5×10⁻³, any combination ofthese ranges, or any range formed from any values from 1.5×10⁻³ to2.5×10⁻³. In other examples, the index difference can be greater orless.

As described herein, the optical device 3000 can include a PIC. The PICcan include an array of VGCs. Also, as described in U.S. PatentApplication Publication 2012/0257857, entitled “HIGH DENSITY OPTICALPACKAGING HEADER APPARATUS”, which is hereby incorporated herein in itsentirety, multiple flexible PROFA couplers (such as the coupler 450),each having multiple optical channels, can be combined together toadvantageously form an optical multi-port input/output (IO) interface.As such, an optical multi-port IO interface can include a plurality ofoptical coupler arrays, at least one of the optical coupler arrays caninclude an optical coupler array 450 as described herein.

With reference now to FIG. 8 and FIG. 9, example cross sectional viewsof the housing structure at a proximity to a first end of a multichanneloptical coupler array are shown. The cross-sectional view is orthogonalto the longitudinal direction or length of the optical coupler array.Some such configurations may have improved cross sectional or transverse(or lateral) positioning of waveguides at the first end allowing forself-aligning waveguide arrangement at a close proximity to a first end(e.g., hexagonal close packed arrangement in a housing structure havingcircular (as shown in FIG. 8) or hexagonal inner cross section) andimproved (precise or near precise in some cases) cross sectionalpositioning of the waveguides at a second end. Such configurations mayalso provide alignment during manufacturing such that the crosssectional positioning of the waveguides at a second end may be moreprecisely disposed as desired.

Although various features of the example optical coupler arrays may bedescribed with respect to FIGS. 8 and 9, any feature described above(for example, in connection with any of the figures or embodimentsdescribe above) can be implemented in any combination with amultichannel optical coupler array. For example, any of the featuresdescribed with respect to FIGS. 1A-5 and 7 may be utilized in amultichannel optical coupler array and may be combined with any featuredescribed with respect to FIGS. 8 and 9.

For example, referring to the example embodiments shown in FIGS. 1A-2D,there are two ends of the coupler array: a first (larger) end, and asecond (smaller) end. The two ends are spaced apart in the longitudinaldirection (along the z direction). For example, in FIG. 1A, the firstend is proximate to position B and the second end is proximate topositions C and D.

In certain embodiments, one of the functions of the first end (proximateto position B) is to encapsulate the waveguides 30A, 32A-1, 32A-2 withincreased or approximate positioning accuracy. For example, the couplerhousing structure 14A at a proximity to the first end (proximate toposition B) may encapsulate, e.g., circumferentially surround a portionof the length of the waveguides 30A, 32A-1, 32A-2, but not necessarilycompletely enclose the ends of the waveguides 30A, 32A-1, 32A-2. In somesuch instances, the waveguides 30A, 32A-1, 32A-2 may or may not extend(e.g., longitudinally) outside the coupler housing structure 14A. InFIG. 1A, proximate the first end, the end of waveguide 30A is disposedwithin the coupler housing structure 14A, but the ends of waveguides32A-1 and 32A-2 extend, e.g., longitudinally (in a direction parallel tothe z-direction) outside of the coupler housing structure 14A. In FIG.2B, proximate the first end, the ends of waveguides 130B-1, 130B-2 aredisposed at an outer cross sectional boundary region of the couplerhousing structure 14A and do not extend, e.g., longitudinally (in adirection parallel to the z-direction) outside of the coupler housingstructure 14A.

In various embodiments, one of the functions of the second end(proximate to positions C and D) is to have the waveguides 30A, 32A-1,32A-2 embedded in a housing structure (e.g., a common housing structurein some instances) with improved (precise or near precise in some cases)cross sectional positioning. For example, the waveguides 30A, 32A-1,32A-2 at a proximity to the second end (proximate to positions C and D)may be embedded, e.g., be circumferentially surrounded by the contiguouscoupler housing structure 14A. In FIG. 1A, proximate the second end, theends of waveguides 30A, 32A-1, 32A-2 are longitudinally disposed at anouter cross sectional boundary region of the coupler housing structure14A. In some embodiments, proximate the second end, one or more ends ofthe waveguides may be disposed within or may longitudinally extendoutside the coupler housing structure 14A.

To achieve improved positioning, some embodiments can include theexample cross sectional configuration of the housing structure shown inFIG. 8 at a proximity to the first end. The cross section is orthogonalto the longitudinal direction or length of the optical coupler array. Asshown in FIG. 8, the coupler array 800 can include a housing structure801 having a transverse (or lateral) configuration of a ring surroundingthe plurality of longitudinal waveguides 805 at a close longitudinalproximity to the first end. A gap, such as an air gap, may separate theplurality of longitudinal waveguides 805 from the surrounding ring. Somesuch configurations may allow for self-aligning waveguide arrangement ata close proximity to a first end (e.g., hexagonal close packedarrangement in a housing structure having circular (as shown in FIG. 8)or hexagonal inner cross section)

In an example configuration shown in FIG. 8, the waveguides 805 are in ahexagonal arrangement. Other arrangements are possible, e.g., square,rectangular, etc.

The ring may have an inner cross section 801 a (in the transversedirection, i.e., orthogonal to the longitudinal direction or length ofthe optical coupler array) that is circular or non-circular. Forexample, the inner cross section 801 a may be circular, elliptical,D-shaped, square, rectangular, hexagonal, pentagonal, octagonal, otherpolygonal shape, etc. The inner cross section 801 a does not necessarilyfollow the arrangement of the waveguides 805. For example, fourwaveguides arranged in a square arrangement can be confined in an innercircular cross section. As another example, as shown in FIG. 8, theinner cross section 801 a is circular, while the waveguides 805 arehexagonally arranged. In some embodiments, a circular inner crosssection, as shown in FIG. 8, may be a preferred shape, which can allowfor a close-pack hexagonal arrangement. Also, other inner crosssectional shapes may also be used, such as square or rectangular, whichcan allow for non-hexagonal waveguide arrangements. In some instances,the inner cross section 801 a may be similar as the arrangement of thewaveguides 805 to reduce empty space. For example, for waveguides 805 ina hexagonal arrangement, the inner cross section 801 a of the ring maybe hexagonal to reduce empty space between the inner cross section 801 aand the waveguides 805.

The outer cross section 801 b (in the transverse direction, e.g.,orthogonal to the longitudinal direction or length of the opticalcoupler array) may be circular or non-circular. For example, the outercross section 801 b may be circular, elliptical, hexagonal, D-shaped(e.g., to provide for passive axial alignment of the coupler since theflat surface allow for an easy rotational alignment), square,rectangular, pentagonal, octagonal, other polygonal shape, etc. In FIG.8, the outer cross section 801 b (e.g., circular) follows the shape ofthe inner cross section 801 a (e.g., circular). However, in someembodiments, the outer cross section 801 b need not be similar as theinner cross section 801 a. One of the functions of the inner crosssectional shape is to allow for an improvement in the transversepositional accuracy at the proximity to the second end, while one of thefunctions of the outer cross sectional shape is to allow for a passiveaxial alignment of the coupler (e.g., the alignment can be done withoutlaunching light into the coupler). In some configurations it may bepreferred to substantially preserve the outer cross sectional shape fromthe first end to the second end to facilitate the passive alignment atone of the ends or at both ends of the coupler array.

FIG. 9 shows another example cross sectional configuration of thehousing structure at a proximity to the first end. As shown in FIG. 9,the coupler array 850 can include a housing structure 851 having aconfiguration of a structure (e.g., a contiguous structure in somecases) with a plurality of holes 852. At least one of the holes 852 maycontain at least one of the longitudinal waveguides 855. A gap, such asan air gap, may separate the plurality of longitudinal waveguides 855from the surrounding housing structure 851. Similarly to the descriptionrelated to the example shown in FIG. 8, the outer cross section may becircular, elliptical, hexagonal, D-shaped, square, rectangular,pentagonal, octagonal, other polygonal shape, etc. Some of suchconfigurations may allow for passive alignment at one of the ends or atboth ends of the coupler array. While the example configuration shown inFIG. 8 may allow for simpler fabrication in some cases, the exampleconfiguration shown in FIG. 9 may allow for arbitrary transversewaveguide positioning.

FIG. 9 shows an example configuration with six holes 852, yet othernumber of holes is possible. The holes 852 in this example configurationmay be isolated or some or even all holes 852 may be connected. Forexample, as shown in FIG. 9, a first hole 852-1 is isolated from asecond hole 852-2. However, in some configurations, the first hole 852-1may be connected to at least one second hole 852-2. The arrangement ofthe holes 852 is shown as a 3×2 array, yet other arrangements arepossible. For example, the hole arrangement pattern may be hexagonal,square, rectangular, or defined by an XY array defining positions of theholes in the transverse plane.

FIG. 9 shows all the holes 852 with a waveguide 855 illustrated as avanishing core (VC) waveguide. However, while at least one of thewaveguide in this example is a VC waveguide, one or more of the holes852 may include a non-vanishing core (Non-VC) waveguide. The VC orNon-VC waveguide 855 can include any of the waveguides described herein,e.g., single mode fiber, multi-mode fiber, polarization maintainingfiber, etc. In some embodiments, one or more of the holes 852 may beempty, or populated with the other (e.g., non-waveguide) material, e.g.,to serve as fiducial marks. One or more of the holes 852 may bepopulated with a single waveguide 855 (in some preferred configurations)as shown in FIG. 9 or with multiple waveguides 855. Depending on thedesign, one or more of the holes 852 may be identical or different thananother hole 852 to accommodate, for example, waveguides 855 ofdifferent shapes and dimensions (e.g., cross sectional shapes,diameters, major/minor elliptical dimensions, etc.). The cross sectionsof the holes 852 may be circular or non-circular. For example, the crosssection may be circular, elliptical, hexagonal or D-shaped (e.g., toprovide for passive axial alignment of polarization maintaining (PM)channels), square, rectangular, pentagonal, octagonal, other polygonalshape, etc. As illustrated, in many cases, the cross section of the hole852 at close proximity to the first end is larger than the cross sectionof the waveguides 855 such that a gap is disposed between an innersurface 851 a of the coupler housing structure 851 and the waveguide855.

The coupler housing structure (e.g., 801 in FIG. 8 or 851 in FIG. 9) caninclude a medium from a wide range of materials as described herein. Asalso described herein, the medium of the coupler housing structure 801,851 can have refractive index (N-4). The medium can be a transverselycontiguous medium. This can allow for a robust housing structure withimproved transverse positioning accuracy in some embodiments. In someembodiments, the total volume of the medium of the coupler housingstructure 801, 851 can be greater than a total volume of all the innerand outer cores of the VC waveguides confined within the coupler housingstructure 801, 851 to provide that in some embodiments, all VCwaveguides are reliably embedded in the housing structure allowing forstable performance).

In certain embodiments, the example configurations shown in FIG. 8 andFIG. 9 may allow for improved manufacturability of the devices withimproved cross sectional (transverse) positioning of the waveguidese.g., at the second end. This transverse position, may for example, bedefined in the x and/or y directions, while z is the direction along thelength coupler array (e.g., from the first end to the second end). Invarious fabrication approaches, the assembly, comprising the waveguides(e.g., 805 in FIGS. 8 and 855 in FIG. 9) and coupler housing structure(e.g., 801 in FIG. 8 or 851 in FIG. 9), may be heated and drawn to forma second end as shown in the lateral cross sectional views shown inFIGS. 3A-3L. Referring to FIG. 8, the waveguides 805 can be insertedinto the coupler housing structure 801 having a configuration of a ring(in the cross section orthogonal to the longitudinal direction or lengthof the optical coupler array, e.g., in the x-y plane shown). Asdescribed above, a gap such as an air gap can be disposed between thecoupler housing structure 801 and the waveguide 805 to permit lateralmovement (in x and/or y directions) of the waveguide with respect to thecoupler housing structure 801. Referring to FIG. 9, one or morewaveguides 855 can be inserted into the coupler housing structure 851having a plurality of holes 852 (e.g., as seen in the cross sectionorthogonal to the longitudinal direction or length of the opticalcoupler array, e.g., in the x-y plane shown) where the waveguides 855can be passively aligned within the housing structure 851. A gap such asan air gap can be disposed between the coupler housing structure 851 andthe waveguide 855 to permit transverse movement (in x and/or ydirections) of the waveguide with respect to the coupler housingstructure 851. In the case of close packed waveguide arrangement (e.g.,hexagonal), this ability to move can result in more precise crosssectional positioning at the second end after manufacturing.

Referring to FIG. 1A, the coupler array can include a plurality oflongitudinal waveguides 30A, 32A-1, 32A-2 with at least one VC waveguide30A having an inner core 20A and an outer core 22A. The inner core 20A,the outer core 22A, and the spacing between the plurality of waveguides30A, 32A-1, 32A-2 can reduce (e.g., simultaneously and gradually in somecases) from the first end (proximate to position B) to the second end(proximate to positions C and D), e.g., from S-1 to S-2. In variousembodiments, the cross sectional configuration at the first end(proximate position B) is shown as in FIG. 8 or FIG. 9, while the crosssectional configuration at the second end (proximate positions C and D)can be shown in FIGS. 3A-3L or FIG. 7. In some embodiments, proximate tothe second end, there is substantially no gap between the couplerhousing structure and the waveguides, some gaps being filled by housingmaterial and some gaps being filled by waveguide cladding material. As aresult of the described cross sectional configuration at the first end,the cross sectional or transverse positioning of the waveguides at thesecond end can be improved. The waveguides at the second end can thus beproperly aligned in the transverse direction (e.g., x and/or ydirection) with an optical device.

With reference now to FIG. 10 and FIG. 11, further example embodimentsof optical coupler arrays 4000, 5000 are shown. The coupler arrays 4000,5000 can be configured to couple to and from a plurality of opticalfibers, such as to and from optical fibers with different mode fieldsand/or core sizes. In some instances, the coupler arrays 4000, 5000 canbe configured to provide coupling between a set of individual isolatedoptical fibers 2000 and an optical device 3000 having at least oneoptical channel allowing for propagation of more than one optical mode.In some preferred embodiments, all isolated optical fibers 2000 can beidentical (or some different in some instances) and the optical device3000 can include at least one few-mode fiber, multimode fiber, multicoresingle mode fiber, multicore few-mode fiber, and/or multicore multimodefiber. Compared to certain embodiments described herein with respect toFIGS. 1A-5, various embodiments 4000, 5000 can include a furtherreduction of the taper diameter, which can allow light to escape theouter core 4120, 5120 and propagate in a combined waveguide 4150, 5150,formed by at least two neighboring cores. Accordingly, variousembodiments described herein can be configured to optically couplebetween fibers with dissimilar mode fields and/or core shapes or sizes.Advantageously, some embodiments of the coupler arrays can improveand/or optimize optical coupling between one or more of single modefibers, few-mode fibers, multimode fibers, multicore single mode fibers,multicore few-mode fibers, and/or multicore multimode fibers.

Although various features of the example coupler arrays will now bedescribed with respect to FIGS. 10 and 11, any described feature can beimplemented in any combination with the coupler arrays described withrespect to FIGS. 1A-5 and 7. Further, any feature described with respectto FIGS. 1A-5 and 7 may be combined with any feature described withrespect to FIGS. 10 and 11. For instance, the example coupler arrays4000, 5000 are illustrated utilizing housing structures 4060, 5060similar to the housing structures 801, 851 shown in FIGS. 8-9. In theseexamples, the cross sectional configuration of the housing structure4060, 5060 may include a structure with a plurality of holes (e.g.,multi-hole) as shown in FIG. 10, or may include one hole (e.g.,single-hole surrounded by a ring), as shown in FIG. 11. However, otherhousing structures can also be used. For example, the housing structuresdescribed with respect to FIGS. 1A-5 and 7 may be used.

Referring to FIG. 10, certain embodiments of a multichannel opticalcoupler array 4000 can include an elongated optical element 4001 havinga first end 4010, an intermediate location or cross section 4050, and asecond end 4020. The optical element 4001 can include a coupler housingstructure 4060 and a plurality of longitudinal waveguides 4100 disposedin the housing structure 4060. The waveguides 4100 can be arranged withrespect to one another in a cross-sectional geometric waveguidearrangement. In FIG. 10, the example cross-sectional geometric waveguidearrangements of the waveguides 4100 for the first end 4010, theintermediate cross section 4050, and the second end 4020 are shown. Asillustrated by the shaded regions within the cross sections and as willbe described herein, light can be guided through the optical element4001 from the first end 4010, through the intermediate cross section4050, and to the second end 4020.

As shown in FIG. 10, proximally (e.g. proximately) to the first end4010, the housing structure 4060 (e.g., a common single coupler housingstructure in some cases) can have a cross sectional configuration of astructure (e.g., transversely contiguous structure in some cases) with aplurality of holes 4062. FIG. 10 shows an example configuration withthree circular holes 4062-1, 4062-2, 4062-3. However, the shape of theholes, number of holes, and/or arrangement of the holes are notparticularly limited and can include any other shape, number, and/orarrangement including those described with respect to FIG. 9. At leastone of the holes 4062 may contain at least one of the longitudinalwaveguides 4100. A gap, such as an air gap, may separate the pluralityof longitudinal waveguides 4100 from the surrounding housing structure4060 proximally to the first end 4010. In some embodiments, there may besubstantially no gap between the coupler housing structure 4060 and thewaveguides 4100 at the intermediate location 4050 and/or at the secondend 4020. For example, one or more gaps may be filled by housingmaterial and/or waveguide cladding material. As described herein, insome embodiments, proximate to the first end 4010, there may be a gapbetween the coupler housing structure 4060 and the waveguides 4100, butproximate to the second end 4020, there may be substantially no gapbetween the coupler housing structure 4060 and the waveguides 4100 (orvice versa). In some embodiments, there may be substantially no gapbetween the coupler housing structure 4060 and the waveguides 4100proximate the first end 4010, the intermediate location 4050, and/or atthe second end 4020.

As described herein, the coupler array 4000 can be operable to opticallycouple with a plurality of optical fibers 2000 and/or with an opticaldevice 3000. The coupler array 4000 can couple with the optical fibers2000 via the plurality of waveguides 4100 proximate the first end 4010(e.g., via a fusion splice 2001), and/or with the optical device 3000via the plurality of waveguides 4100 proximate the second end 4020(e.g., via a fusion splice not shown). In FIG. 10, three waveguides 4100are shown in each of the three holes 4062-1, 4062-2, 4062-3. However,any number of waveguides 4100 for each of the holes 4062 can be used. Insome embodiments, the number of waveguides 4100 may equal the number ofoptical fibers 2000 (e.g., 9 waveguides to couple with 9 opticalfibers). In some other embodiments, the number of waveguides 4100 in atleast one hole may equal the number of optical modes supported by acorresponding few-mode or multi-mode waveguide of the device 3000 (e.g.3 waveguides in each of 3 holes to couple with three 3-mode cores of amulticore fiber). In various embodiments, the waveguides 4100 can bepositioned within each hole 4062 at a spacing (e.g., predetermined insome instances) from one another. In some preferred embodiments of themulti-hole configuration, the individual holes 4062-1, 4062-2, 4062-3may contain all the waveguides (e.g., fibers) intended to couple to atleast one particular core of a few-mode, multimode and/or multicorefiber of an optical device. In some other embodiments, one or moreadditional fibers and/or dummy fibers (e.g., which might not guidelight) may be utilized to create a particular geometrical arrangement ofthe active, light-guiding fiber waveguides.

In various embodiments, the plurality of waveguides 4100 can have acapacity for at least one optical mode (e.g., a predetermined mode fieldprofile in some cases). The plurality of waveguides 4100 can include atleast one vanishing core (VC) waveguide 4101. FIG. 10 illustrates all ofthe waveguides 4100 as VC waveguides. However, one or more Non-VCwaveguides may also be used. As described herein, the VC waveguide 4101can include an inner core (e.g., an inner vanishing core) 4110, an outercore 4120, and an outer cladding 4130 with refractive indices N-1, N-2,and N-3 respectively. The outer core 4120 can longitudinally surroundthe inner core 4110, and the outer cladding 4130 can longitudinallysurrounding the outer core 4120. As described herein, the relativemagnitude relationship between the refractive indices of the inner core4110, outer core 4120, and the outer cladding 4130 can advantageously beN-1>N-2>N-3.

In various embodiments, the housing structure 4060 can surround thewaveguides 4100. The coupler housing structure 4060 can include a medium4140 having an index of refraction N-4. The medium 4140 can include anyof those described herein. In some instances, a total volume of themedium 4140 of the coupler housing structure 4060 can be greater than atotal volume of all the inner and outer cores 4110, 4120 of the VCwaveguides confined within the coupler housing structure 4060. In someexamples, the waveguides 4100 may be embedded in the housing structure4060 (e.g., proximate the second end 4020).

In certain embodiments, the inner core 4110 waveguide dimensions, theouter core 4120 waveguide dimensions, refractive indices, and/ornumerical apertures (NAs) are selected to increase and/or optimizecoupling to the individual fibers 2000. In various embodiments, theouter core 4120 waveguide dimensions, refractive indices, NAs, and/orthe cladding 4130 dimensions are selected to increase and/or optimizecoupling to the optical device 3000. Various embodiments describedherein can also include reflection reduction features of thepitch-reducing optical fiber array described in U.S. application Ser.No. 14/677,810, entitled “OPTIMIZED CONFIGURABLE PITCH REDUCING OPTICALFIBER COUPLER ARRAY”, which is incorporated herein in its entirety. Forpolarization control, some of the outer cores 4120 can be made with anon-circular cross section (e.g., elliptical as shown in FIG. 10) and aparticular orientation of the outer cores 4120 can be used to increaseand/or optimize optical coupling. Various embodiments described hereincan also include features of any of the optical polarization modecouplers described in U.S. application Ser. No. 15/617,684, entitled“CONFIGURABLE POLARIZATION MODE COUPLER”, which is incorporated hereinin its entirety.

In some embodiments, the inner core 4110 size, the outer core 4120 size,the cladding 4130 size, and/or the spacing between the waveguides 4100can reduce (e.g., simultaneously and gradually in some instances) alongthe optical element 4001 from the first end 4010 to an intermediatelocation or cross section 4050. In some embodiments, a predeterminedreduction profile may be used. In the example shown in FIG. 10, at theintermediate location 4050, the inner core 4110 may be insufficient toguide light therethrough and the outer core 4120 may be sufficient toguide at least one optical mode (e.g., spatial mode).

In some embodiments, each core of a waveguide 4100 can have a capacityfor at least one optical mode (e.g., single mode, few-mode, ormulti-mode). For example, at the first end 4010, the VC waveguide 4101can support a number of spatial modes (M1) within the inner core 4110.At the intermediate location 4050, in various embodiments, the innercore 4110 may no longer be able to support all the M1 modes (e.g.,cannot support light propagation). However, in some such embodiments, atthe intermediate location 4050, the outer core 4120 can be able tosupport all the M1 modes (and in some cases, able to support additionalmodes). In this example, light traveling within the inner core 4110 fromthe first end 4010 to the intermediate location 4050 can escape from theinner core 4110 into the outer core 4120 such that light can propagatewithin the outer core 4120.

In some embodiments, the inner core 4110 size, the outer core 4120 size,the cladding 4130 size, and/or the spacing between the waveguides 4100can be further reduced (e.g., simultaneously and gradually in someinstances) along the optical element 4001 from the intermediate location4050 to the second end 4020. In the example shown in FIG. 10, at thesecond end 4020, the outer core 4120 may be insufficient to guide lighttherethrough.

In certain embodiments, at the intermediate location 4050, the VCwaveguide 4101 can support all the M1 modes within the outer core 4120.At the second end 4020, the outer core 4120 may be no longer able tosupport all the M1 modes (e.g., cannot support light propagation).However, in some such embodiments, at the second end 4020, a combinedcore 4150 of at least two cores may be able to support all the M1 modesof all waveguides 4101 combined (and in some cases, able to supportadditional modes). In this example, light traveling within the outercore 4120 from the intermediate location 4050 to the second end 4020 canescape from the outer core 4120 into a combined waveguide 4150 formed byat least two outer cores (e.g., two or more neighboring cores) such thatlight can propagate within the combined cores. In the example shown inFIG. 10, each of the combined waveguides 4150 is formed by three outercores. However, in some embodiments, the combined waveguides 4150 may beformed with another number of outer cores.

It would be appreciated that light travelling from the second end 4020to the first end 4010 can behave in the reverse manner. For example, insome embodiments, light can move from the combined waveguide 4150 formedby at least two neighboring outer cores into the at least one outer core4120 proximally to the intermediate cross section 4050, and can movefrom the outer core 4120 into corresponding inner core 4110 proximallyto the first end 4010. In the example shown in FIG. 10, each of thecombined waveguides 4150 can support three propagation modes. Travellingfrom the second end 4020 to the first end 4010, each propagation modecan be coupled to a corresponding outer core 4120 proximally to theintermediate cross section 4050 and move from the outer core 4120 into acorresponding inner core 4110 proximally to the first end 4010.

Referring now to FIG. 11, the example embodiment 5000 includes similarfeatures as the example embodiment 4000 shown in FIG. 10. One differenceis that the cross sectional configuration of the housing structure 5060includes a structure with a single hole 5062 instead of a plurality ofholes 4062. Similar to the example embodiment 4000 shown in FIG. 10, theoptical element 5001 can include a coupler housing structure 5060 (e.g.,including a medium 5140) and a plurality of longitudinal waveguides 5100disposed in the housing structure 5060. The waveguides 5100 can bearranged with respect to one another in a cross-sectional geometricwaveguide arrangement within the hole 5062. As illustrated, light can beguided through the optical element 5001 from the first end 5010, throughthe intermediate cross section 5050, and to the second end 5020.

As described herein, a gap may separate the plurality of longitudinalwaveguides 5100 from the surrounding housing structure 5060. In someembodiments, there may be substantially no gap between the couplerhousing structure 5060 and the waveguides 5100 proximate theintermediate location 5050 and/or the second end 5020. For example, inFIG. 11, although a gap is shown proximate the second end 5020, inpreferred embodiments, there may be substantially no gap between thecoupler housing structure 5060 and the waveguides 5100. In someembodiments, there may be substantially no gap between the couplerhousing structure 5060 and the waveguides 5100 proximate the first end5010, the intermediate location 5050, and/or the second end 5020.

In various embodiments, the plurality of waveguides 5100 can include atleast one VC waveguide 5101. FIG. 11 illustrates all thirty seven of thewaveguides 5100 as VC waveguides 5101 in a hexagonal arrangement.However, any arrangement may be used. In addition, any number of VCwaveguides, Non-VC waveguides, and/or dummy fibers may be used. Asdescribed herein, one or more dummy fibers may be utilized to create aparticular geometrical arrangement of the active, light-guiding fiberwaveguides. As described herein, the VC waveguide 5101 can include aninner vanishing core 5110, an outer core 5120, and an outer cladding5130.

In certain embodiments, the inner core 5110 waveguide dimensions, theouter core 5120 waveguide dimensions, the cladding 5130 dimensions,refractive indices, and/or the numerical apertures (NAs) can be selectedto increase and/or optimize coupling to the individual fibers 2000and/or optical device 3000. In some embodiments, the inner core 5110size, the outer core 5120 size, the cladding 5130 size, and/or thespacing between the waveguides 5100 can reduce along the optical element5001 from the first end 5010 to the second end 5020. In the exampleshown in FIG. 11, at the intermediate location 5050, the inner core 5110of certain waveguides 5100 may be insufficient to guide lighttherethrough and the outer core 5120 of certain waveguides 5100 may besufficient to guide at least one optical mode (e.g., spatial mode). Inthis example, proximate the second end 5020, the outer core 5120 may beinsufficient to guide light therethrough. Accordingly, in someembodiments, light traveling within the outer core 5120 from theintermediate location 5050 to the second end 5020 can escape from theouter core 5120 into a combined waveguide 5150 formed by at least twoouter cores (e.g., two or more neighboring cores) such that light canpropagate within the combined cores. In the example shown in FIG. 11,although each of the combined waveguides 5150 is formed by three outercores, the combined waveguides 5150 may be formed by another number ofouter cores. The remaining cores (e.g., cores of waveguides or dummyfibers) may or may not guide light. Light travelling from the second end5020 to the first end 5010 can behave in the reverse manner.

Optical fiber arrays can be used in coherent or incoherent beamcombining applications. Various multichannel optical couplers includingfiber arrays described herein can address one or more of the followingdisadvantages of other beam combining devices:

-   -   1. Coherent combining multiple lasers can use multiple        individual back reflectors. The reflectors may be fabricated as        a single, large area reflector accommodating multiple channels,        or fabricated as terminations of individual channels. They may        be made by depositing mirrors on the fiber faces or by creating        fiber Bragg gratings (FBG) in the fibers. The reflectors can be        costly, have some deviation from 100% reflectivity, and may be        degraded or damaged due to exposure to high optical power.    -   2. Different channels can have different optical lengths, which        may use complex active length adjustment for phase locking.    -   3. The combined cavity can have multiple competing supermodes,        some of which may have to be suppressed.

FIG. 12 schematically illustrates an example multichannel opticalcoupler 6000 that can be used in coherent or incoherent beam combiningapplications. The example multichannel optical coupler 6000 can includean output optical coupler array 6010 and a plurality of optical fibers6034 (e.g., 6034-1, 6034-2, 6034-3, 6034-4, 6034-5, 6034-6, 6034-7,6034-8, 6034-9, 6034-10). At least two of the optical fibers (e.g.,6034-1 and 6034-4; 6034-5 and 6034-8; and 6034-6 and 6034-10) can beconnected together at an end opposite the output optical coupler array6010.

In various implementations, the output optical coupler array 6010 caninclude any optical coupler array known in the art or yet to bedeveloped. The output optical coupler array can include any opticalcoupler array described herein, e.g., any optical coupler array in FIGS.1A-11. As an example, in some instances, the output optical couplerarray can include a pitch reducing optical fiber array (PROFA) asdescribed herein.

The output optical coupler array 6010 can have a first end 6010A and asecond end 6010B. In some examples, the output optical coupler array6010 can taper (e.g., decrease or increase in cross sectional area) fromthe first end 6010A to the second end 6010B. With reference to FIG. 12,the output optical coupler array 6010 can be optically connected at thefirst end 6010A to a plurality of optical fibers 6034. The outputoptical coupler array 6010 can be configured to receive light at thefirst end 6010A from the optical fibers 6034, and output the light 6040at the second end 6010B. In this example, one of three cases may beimplemented based on the desired output: (1) the light can be keptisolated in different channels of the array, (2) the array channels canbe weakly coupled, and (3) the array channels can be strongly coupled.As described herein, the light 6040 from the plurality of optical fibers6034 can be sent to an optical device. The output optical coupler array6010 can also receive light at the second end 6010B (e.g., from anoptical device) and output the light at the first end 6010A to theoptical fibers 6034. In some examples, the output optical coupler array6010 can be optically connected at the second end 6010B to the opticalfibers 6034 to receive light from at least one of optical fibers 6034and output the light at the first end 6010A.

In FIG. 12, ten optical fibers (e.g., 6034-1, 6034-2, 6034-3, 6034-4,6034-5, 6034-6, 6034-7, 6034-8, 6034-9, 6034-10) are illustrated,although the number of optical fibers is not particularly limited (e.g.,2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 40, 50, 75, 80, 90, 100,etc., or any range formed by any such values). The optical fiber 6034can be any optical fiber known in the art or yet to be developed. Forexample, the optical fibers 6034 can include single mode fibers,few-mode fibers, multimode fibers, polarization maintaining fibers,and/or any combination thereof. As shown in FIG. 12, the optical fibers6034 can include one or more gain blocks 6050 configured to allow lightamplification. In some designs, a gain block 6050 can be composed of apump fiber 6051, e.g., a section of an active or doped fiber (single- ordouble-clad). The gain block 6050 can also include at least onepump-signal combiner 6052, and at least one pump light source 6053,e.g., at the end of the pump fiber 6051. In the example of FIG. 12, apair of pump-signal combiners 6052 with corresponding pump sources 6053is shown at both ends of the pump fiber 6051 for one or more (possiblyeach) gain block 6050.

The optical fibers 6034 can have a first end 6034A and a second end6034B. In FIG. 12, the first end 6034A is optically connected to thefirst end 6010A of the output optical coupler array 6010. In variousembodiments, at least two of the optical fibers 6034 can be connectedtogether (e.g., forming a connection 6036) at an end opposite the outputoptical coupler array 6010 (e.g., proximate the second end 6034B of theoptical fibers 6034). In FIG. 12, optical fibers 6034-1 and 6034-4 areconnected together, optical fibers 6034-5 and 6034-8 are connectedtogether, and optical fibers 6034-6 and 6034-10 are connected together6036 proximate the back-end 6034B. In some instances, the optical fiberscan be connected together via a fusion splice or a section of a similartype of fiber can be used for the connection. In some instances, one ormore fibers can form a loop.

In various embodiments, by being connected together, individual fiberscan form channels with no fiber reflectors at the back of the connectedchannels 6036. In some instances, wavelength selective elements, such asfiber Bragg gratings (FBGs), can still be used in the connectedchannels. In some instances, modulating elements, such as, for example,amplitude or phase modulators (fiber- or chip-based), for Q-switching,for example, may be used in the connected channels. In some examples,the output optical coupler array 6010 (e.g., a PROFA) may include areflector (e.g., a Talbot mirror) to form a connected Talbot cavity, asdescribed in U.S. Pat. No. 9,851,510, entitled “PHASE LOCKING OPTICALFIBER COUPLER”, issued Dec. 26, 2017, which is hereby incorporatedherein by reference in its entirety. For example, a reflective surfaceor reflector may be included at the second end 6010B of the opticalcoupler array 6010. This reflective surface or mirror may comprise acommon reflector, reflective surface, or mirror that is common tomultiple channels and cores or be included for multiple channels orcores.

In some implementations, one or more optical fibers (e.g., 1, 2, 3, 4,5, 6, 7, 8, 9, 10, etc. or any ranges formed by any such values) mightnot be connected with another optical fiber at the end 6034B oppositethe optical coupler array 6010. An unconnected fiber can be suitable forpassive or active phase locking. For example, reflectors, wavelengthselective elements (e.g., FBGs), and/or modulating elements can be usedin the unconnected ends 6034B. However, terminating the back end of thefiber array with connection 6036 can allow for the following benefits:

-   -   1. The number of the reflectors can be reduced. In some        embodiments, the reflectors can be completely eliminated such as        if there is an even number of channels and all of them are        interconnected.    -   2. In some instances, the replacement of back-reflectors with        connections can effectively correspond to a significantly higher        efficiency of substantially no light loss (e.g., substantially        100% efficiency). In addition, the power handling limit can be        similar (e.g., substantially identical in some instances) to the        fiber itself. For example, the optical power exposure level        would not be limited by the level that may degrade a reflector.    -   3. In some instances, connecting some channels together can        change the property of the laser cavity, making it more similar        to a Sagnac loop rather than a Fabry-Perot resonator. In        general, a Sagnac interferometer can be more stable with respect        to the phase fluctuations compared to a Fabry-Perot        interferometer.    -   4. From the phase locking prospective, the effective number of        channels to be locked can be reduced since the connected        channels can have the same optical length in some instances.        This can lead to either less complex electronics in the case of        active phase locking or to a more efficient device in the case        of passive phase locking. For example, connected channels have        the same optical length, so if the array is fully connected, the        number of channels with different length can be reduced two        times. Thus, if there is a passive phase locking element        normally capable of locking N channels, certain implementations        can lock 2N channels. The complexity of the active phase locking        electronics can also be reduced two times, since it is        proportional to the number of channels.    -   5. The connection map may be selected in such a way that        undesired cavity supermodes can be reduced, substantially        suppressed, and/or eliminated. For many applications, a        single-mode, for example, an all coherent, phase locked        operation can be highly desirable. Achieving this mode over a        large pump power range can use a large threshold difference        between desired (in-phase, for example) and all undesired        (out-of-phase, for example) supermodes. Since different        supermodes have different phase and/or amplitude variations        across the channels, the appropriately selected connection map        can favor the preselected desired supermode and suppress the        undesired modes.    -   6. Various implementations do not require all channels to be        connected to be beneficial and can be compatible with developed        techniques. For example, unconnected channel(s) can be used for        wavelength selectivity or modulation.

Some embodiments can advantageously generate a single polarization modeoutput from the fiber array. For example, in some examples, one or morepolarization beam splitters and/or isolators can be used in connectedchannels. FIG. 13 schematically illustrates an example multichanneloptical coupler 7000 creating a single polarization mode output. Theexample multichannel optical coupler 7000 can include an output opticalcoupler array 7010. The output optical coupler array 7010 can includeany polarization maintaining (PM) coupler array. In some instances, thePM coupler array can include a PM PROFA as described herein. In someexamples, the output optical coupler array 7010 can be tapered. Thecoupler array 7010 can output light of a certain polarization mode. Withreference to FIG. 13, the example coupler array 7010 is shown to allowonly right-circularly polarized (RCP) light to exit at the second end7010-2. The reflected part of this light (e.g., via Fresnel reflection)becomes the left-circularly polarized (LCP) light to exit at a first end7010-1.

The coupler array 7010 can be connected to a plurality of optical fibers7034. For simplicity, this example shows only two optical fibers 7034forming two channels, although additional optical fibers/channels can beused. The optical fibers 7034 can include one or more polarizationconverters 7045 (e.g., circular-to-linear or linear-to-circularconverters), gain blocks 7050, polarization beam splitters 7060, and/orisolators 7065. The optical fibers 7034 can be connected together at anend opposite the optical coupler array 7010 such as to form a connection7036. In some instances, the optical fibers 7034 can be connected with90 degree splices.

With continued reference to FIG. 13, the circularly polarized light fromthe optical coupler array 7010 can be converted to linearly polarizedlight by the polarization converters 7045 (e.g., a circular-to-linearconverter). Light of a certain linear polarization mode (e.g., fast) canpass through the gain blocks 7050, the polarization beam splitters 7060,and isolators 7065. The linear polarized light can convert to anotherpolarization mode (e.g., slow) due to the connection 7036 (e.g., a90-degree splice), where it once again can pass through the polarizationbeam splitters 7060, gain blocks 7050, converters 7045, and couplerarray 7010. Upon exiting the PM coupler array 7010, only a singlepolarization mode can be outputted (e.g., RCP light in this example). Insome such examples, the multichannel optical coupler 7000 canadvantageously generate a single polarization mode without axial channelalignment, as described for example in U.S. Patent ApplicationPublication No. 2017/0219774, entitled “POLARIZATION MAINTAINING OPTICALFIBER ARRAY”, which is hereby incorporated herein by reference in itsentirety. Other examples are possible.

Referring now to FIG. 14, a set 500 of example refractive indexprofiles, each comprising a different back reflection loss reductionscenario—Optimized Refraction Index Profile “ORIP” (ORIP-a to ORIP-c),corresponding to a particular coupler array configuration. ORIP-a toORIP-c are shown by way of example for a coupler array 502 positionedbetween a plural optical fiber 504 and an optical device 506, withinterfaces of each with respective ends of the coupler array 502 shownas Interface 1 and Interface 2.

The profile shown as ORIP-a results in a substantial back reflection atthe Interface 1 and suppressed back reflection at the Interface 2. Theprofile shown as ORIP-b results in a substantially no back reflection atthe Interface 1 and significant back reflection at the Interface 2. Theprofile shown as ORIP-c results in an reduced, e.g., optimized, totalback reflection from both Interfaces 1 and 2, balancing the reduction ofback reflection at each (for example with the goal of reducing themaximum back reflection for the higher reflection or with the goal ofreducing the sum of reflections from Interfaces 1 and 2) Interface ofInterfaces 1, 2.

In some instances, to achieve the result, shown in profiles ORIP-b orORIP-c, the coupler array 502 vanishing core waveguide refractive indexN-3 can be lower than the refractive index N_(of) of the cladding of theplural optical fiber 504. Thus for example, if the cladding of theplural optical fiber 504 is made of pure silica, then N-3 can be lowerthan the refractive index of the pure silica, and the outer cladding ofthe vanishing core waveguide longitudinally surrounding the outer corecan comprise another material, for example, fluorine doped silica.

While the baseline refractive index N_(of) is shown to be the same forthe plural optical fiber 504 and the optical device 506, it should benoted that the value of the plural optical fiber 504 baseline refractiveindex N_(of) can be different from the baseline refractive index valueN_(of) of the optical device 506.

The above design, e.g., optimization, techniques can be readily andadvantageously applied to various embodiments of the coupler array suchas shown in FIGS. 1A to 2D, and in FIGS. 4, 5 (in which the Interface-1and Interface-2, corresponding to the Optimization Profile Set 500, areshown as INT-1, and INT-2 respectively), and in FIGS. 7, 10, 11.

FIG. 15 illustrates a set 600 of example refractive index profiles.Other examples are possible. As illustrated in FIG. 15, a coupler array602 comprising at least one vanishing core waveguide can be coupled at afirst end to an optical fiber 604 and at a second end to an opticaldevice 606. The optical fiber 604 can have a core refractive indexNcoreFiber, a cladding refractive index NcladdingFiber, and apropagating mode with an effective refractive index NeffFiber. Theoptical device 606 can have a mode propagating in a waveguide with acore refractive index NcoreDevice, a cladding refractive indexNcladdingDevice, and an effective refractive index NeffDevice. Thevanishing core waveguide in the coupler array 602 can have an innervanishing core with a first refractive index (N-1), an outer core with asecond refractive index (N-2), and an outer cladding having a thirdrefractive index (N-3). The vanishing core waveguide can have aneffective refractive index Neff1 at the first end and Neff2 at thesecond end. In various designs, the vanishing core waveguide cancomprise a refractive index profile in which the first refractive index(N-1), the first inner core size, the second inner core size, the secondrefractive index (N-2), the first outer core size, the second outer coresize, and the third refractive index (N-3) are configured to reduce atan optical fiber interface and/or at an optical device interface, backreflection of the light traveling in the first direction from theplurality of optical fibers to the optical device, and/or in the seconddirection from the optical device to the plurality of optical fibers.

As shown for index profile a, Neff2 can be substantially equal toNeffDevice. In various implementations, substantially equal regardingindices can mean that the two index values are within 5% of each other(e.g., depending on the application, within 1%, within 2%, within 3%,within 4%, or within 5% of each other). For example, in some designs,Neff2 can be within 1%, within 2%, within 3%, within 4%, or within 5% ofNeffDevice. In some instances, Neff1 can be not equal to NeffFiber. Invarious implementations, two index values can be not substantially equalif they are different by at least 5% of each other (e.g., depending onthe application, different by at least 5%, different by at least 6%,different by at least 7%, different by at least 8%, different by atleast 9%, or different by at least 10% of each other). For example, insome designs, Neff1 can be different by at least 5%, different by atleast 6%, different by at least 7%, different by at least 8%, differentby at least 9%, or different by at least 10% of NeffFiber. In somedesigns, two index values may not be equal. For example, two indexvalues may be not equal by at least 1%, by at least 2%, by at least 3%,by at least 4%, etc. of each other. In some instances, Neff1 can be notequal by at least 1%, by at least 2%, by at least 3%, by at least 4%,etc. of NeffFiber,

In some implementations, Neff1 can be larger than NeffFiber. In someinstances, N-3 can be substantially equal to NcladdingFiber, N-2 can besubstantially equal NcoreDevice, and N-1 can be substantially equal to(N-2)+(NcoreFiber-NcladdingFiber). In various designs, the vanishingcore waveguide can comprise a refractive index profile in which thefirst refractive index (N-1), the first inner core size, the secondinner core size, the second refractive index (N-2), the first outer coresize, the second outer core size, and the third refractive index (N-3)are configured to reduce at an optical device interface, back reflectionof the light traveling in the first direction from the plurality ofoptical fibers to the optical device, and/or in the second directionfrom the optical device to the plurality of optical fibers.

As shown for index profile b, Neff1 can be substantially equal toNeffFiber while Neff2 is not equal (e.g., not equal by at least 1%) ornot substantially equal (e.g., within 5%) to NeffDevice. In someimplementations, for example, Neff2 can be smaller than NeffDevice. Insome instances, the third refractive index (N-3) in at least one of thevanishing core waveguides can be lower than NcladdingFiber. N-1 can besubstantially equal to NcoreFiber, N-2 can be substantially equalNcladdingFiber, and N-3 can be substantially equal to(N-2)−(NcoreDevice-NcladdingDevice). In various designs, the vanishingcore waveguide can comprise a refractive index profile in which thefirst refractive index (N-1), the first inner core size, the secondinner core size, the second refractive index (N-2), the first outer coresize, the second outer core size, and the third refractive index (N-3)are configured to reduce at an optical fiber interface, back reflectionof the light traveling in the first direction from the plurality ofoptical fibers to the optical device, and/or in the second directionfrom the optical device to the plurality of optical fibers.

As shown for index profile c, Neff1 can be larger than NeffFiber andNeff2 can be smaller than NeffDevice. In some instances, the thirdrefractive index (N-3) in at least one of the vanishing core waveguidescan be lower than the NcladdingFiber. In some instances, N-3 can besmaller than NcladdingFiber, N-2 can be substantially equal to(N-3)+(NcoreDevice-NcladdingDevice), and N-1 can be substantially equalto (N-2)+(NcoreFiber-NcladdingFiber). In some designs, the vanishingcore waveguide can comprise a refractive index profile in which thefirst refractive index (N-1), the first inner core size, the secondinner core size, the second refractive index (N-2), the first outer coresize, the second outer core size, and the third refractive index (N-3)can be configured to reduce at an optical fiber interface and at anoptical device interface, a sum of back reflections of the lighttraveling in the first direction from the plurality of optical fibers tothe optical device and/or in the second direction from the opticaldevice to the plurality of optical fibers.

In various implementations, the coupler array 602 can be configured toincrease optical coupling to the optical device 606 at the second end.In some instances, the optical device 606 can comprise afree-space-based optical device, an optical circuit having at least oneinput/output edge coupling port, or an optical circuit having at leastone optical port comprising vertical coupling elements. In someinstances, the optical device 606 can comprise a multi-mode opticalfiber, a double-clad optical fiber, a multi-core optical fiber, a largemode area fiber, a double-clad multi-core optical fiber, astandard/conventional optical fiber, or a custom optical fiber. In someinstances, the coupler array 604 can comprise an additional couplerarray.

Thus, while there have been shown and described and pointed outfundamental novel features of the invention as applied to preferredembodiments thereof, it will be understood that various omissions andsubstitutions and changes in the form and details of the devices andmethods illustrated, and in their operation, may be made by thoseskilled in the art without departing from the spirit of the invention.For example, it is expressly intended that all combinations of thoseelements and/or method steps which perform substantially the samefunction in substantially the same way to achieve the same results arewithin the scope of the invention. It is the intention, therefore, to belimited only as indicated by the scope of the claims appended hereto.

What is claimed is:
 1. A multichannel optical coupler array for opticalcoupling of a plurality of optical fibers to an optical device,comprising: an elongated optical element having a first end operable tooptically couple with said plurality of optical fibers and a second endoperable to optically couple with said optical device, and comprising: acommon single coupler housing structure; a plurality of longitudinalwaveguides each positioned at a spacing from one another, each having acapacity for at least one optical mode, each embedded in said commonsingle housing structure proximally to said second end, wherein at leastone of said plurality of longitudinal waveguides is a vanishing corewaveguide configured to be coupled at said first end to one of saidplurality of optical fibers having a propagating mode with an effectiverefractive index NeffFiber and configured to be coupled at said secondend to said optical device having a mode with an effective refractiveindex NeffDevice, said at least one vanishing core waveguide having aneffective refractive index Neff1 for said at least one optical mode atsaid first end and Neff2 at said second end, each said at least onevanishing core waveguide comprising: an inner vanishing core, having afirst refractive index (N-1), and having a first inner core size (ICS-1)at said first end, and a second inner core size (ICS-2) at said secondend; and an outer core, longitudinally surrounding said inner core,having a second refractive index (N-2), and having a first outer coresize (OCS-1) at said first end, and a second outer core size (OCS-2) atsaid second end; and an outer cladding, longitudinally surrounding saidouter core, having a third refractive index (N-3), a first cladding sizeat said first end, and a second cladding size at said second end,wherein said common single coupler housing structure comprises atransversely contiguous medium having a fourth refractive index (N-4)surrounding said plurality of longitudinal waveguides, wherein arelative magnitude relationship between said first, second, and thirdrefractive indices (N-1, N-2, and N-3, respectively), comprises thefollowing magnitude relationship: (N-1>N-2>N-3), wherein a total volumeof said medium of said common single coupler housing structure, isgreater than a total volume of all said vanishing core waveguides innercores and said outer cores confined within said common single couplerhousing structure, wherein said first inner vanishing core size (ICS-1),said first outer core size (OCS-1), and said spacing between saidplurality of longitudinal waveguides, are simultaneously and graduallyreduced, in accordance with a reduction profile, between said first endand said second end along said elongated optical element, until saidsecond inner vanishing core size (ICS-2) and said second outer core size(OCS-2) are reached, wherein said second inner vanishing core size(ICS-2) is selected to be insufficient to guide light therethrough, andsaid second outer core size (OCS-2) is selected to be sufficient toguide at least one optical mode, such that: light traveling in a firstdirection from said first end to said second end escapes from said innervanishing core into said corresponding outer core proximally to saidsecond end, and light traveling in a second direction from said secondend to said first end moves from said outer core into said correspondinginner vanishing core proximally to said first end, wherein said commonsingle coupler housing structure proximally to said first end has across sectional configuration comprising a transversely contiguousstructure with at least one hole, wherein the at least one hole containsat least one of said plurality of longitudinal waveguides creating a gapbetween the coupler housing structure and the at least one of saidplurality of longitudinal waveguides, and wherein the relationshipbetween said Neff1, Neff2, NeffFiber, and NeffDevice is one of: (1)Neff2 is substantially equal to NeffDevice and Neff1 is not equal toNeffFiber; (2) Neff1 is substantially equal to NeffFiber and Neff2 isnot equal to NeffDevice; or (3) Neff1 is larger than NeffFiber and Neff2is smaller than NeffDevice.
 2. The multichannel optical coupler array ofclaim 1, wherein in at least one of said vanishing core waveguidescomprises a refractive index profile in which: said first refractiveindex (N-1), said first inner core size (ICS-1), said second inner coresize (ICS-2), said second refractive index (N-2), said first outer coresize (OCS-1), said second outer core size (OCS-2), and said thirdrefractive index (N-3), are configured to reduce at an optical fiberinterface and/or at an optical device interface, back reflection of thelight traveling in at least one of: in said first direction from saidplurality of optical fibers to said optical device, or in said seconddirection from said optical device to said plurality of optical fibers.3. The multichannel optical coupler array of claim 1, wherein said Neff1is larger than NeffFiber and said Neff2 is substantially equal toNeffDevice.
 4. The multichannel optical coupler array of claim 3,wherein said one of said plurality of optical fibers has a corerefractive index NcoreFiber and cladding refractive index NcladdingFiberand said optical device has a mode with core refractive indexNcoreDevice and cladding refractive index NcladdingDevice, and whereinsaid N-3 is substantially equal to NcladdingFiber, N-2 is substantiallyequal NcoreDevice, and N-1 is substantially equal to(N-2)+(NcoreFiber-NcladdingFiber).
 5. The multichannel optical couplerarray of claim 1, wherein said Neff1 is substantially equal to NeffFiberand said Neff2 is smaller than NeffDevice.
 6. The multichannel opticalcoupler array of claim 5, wherein said one of said plurality of opticalfibers has a cladding refractive index NcladdingFiber, and wherein saidthird refractive index (N-3) in at least one of said vanishing corewaveguides is lower than said NcladdingFiber.
 7. The multichanneloptical coupler array of claim 5, wherein said one of said plurality ofoptical fibers has a core refractive index NcoreFiber and claddingrefractive index NcladdingFiber and said optical device has a mode withcore refractive index NcoreDevice and cladding refractive indexNcladdingDevice, and wherein said N-1 is substantially equal toNcoreFiber, N-2 is substantially equal NcladdingFiber, and N-3 issubstantially equal to (N-2)−(NcoreDevice-NcladdingDevice).
 8. Themultichannel optical coupler array of claim 1, wherein said Neff1 islarger than NeffFiber and said Neff2 is smaller than NeffDevice.
 9. Themultichannel optical coupler array of claim 8, wherein said one of saidplurality of optical fibers has a cladding refractive indexNcladdingFiber, and wherein said third refractive index (N-3) in atleast one of said vanishing core waveguides is lower than saidNcladdingFiber.
 10. The optical coupler array of claim 8, wherein saidone of said plurality of optical fibers has a core refractive indexNcoreFiber and cladding refractive index NcladdingFiber and said opticaldevice has a mode with core refractive index NcoreDevice and claddingrefractive index NcladdingDevice, and wherein said N-3 is smaller thanNcladdingFiber, N-2 is substantially equal to(N-3)+(NcoreDevice-NcladdingDevice), and N-1 is substantially equal to(N-2)+(NcoreFiber-NcladdingFiber).
 11. The multichannel optical couplerarray of claim 8, wherein in at least one of said vanishing corewaveguides comprises a refractive index profile in which: said firstrefractive index (N-1), said first inner core size (ICS-1), said secondinner core size (ICS-2), said second refractive index (N-2), said firstouter core size (OCS-1), said second outer core size (OCS-2), and saidthird refractive index (N-3), are configured to reduce at an opticalfiber interface and at an optical device interface, a sum of backreflections of the light traveling in at least one of: in said firstdirection from said plurality of optical fibers to said optical device,or in said second direction from said optical device to said pluralityof optical fibers.
 12. The multichannel optical coupler array of claim1, wherein the optical coupler array is configured to increase opticalcoupling to said optical device at said second end, wherein said opticaldevice comprises one of: a free-space-based optical device, an opticalcircuit having at least one input/output edge coupling port, or anoptical circuit having at least one optical port comprising verticalcoupling elements.
 13. The multichannel optical coupler array of claim1, wherein the optical coupler array is configured to increase opticalcoupling to said optical device at said second end, wherein said opticaldevice comprises one of: a multi-mode optical fiber, a double-cladoptical fiber, a multi-core optical fiber, a large mode area fiber, adouble-clad multi-core optical fiber, a standard/conventional opticalfiber, or a custom optical fiber.
 14. The multichannel optical couplerarray of claim 1, wherein the optical coupler array is configured toincrease optical coupling to said optical device at said second end,wherein said optical device comprises an additional optical couplerarray.
 15. The multichannel optical coupler array of claim 1, whereinN-3≤N-4.
 16. The multichannel optical coupler array of claim 1, whereinproximate the second end, the coupler array comprises substantially nogap between the coupler housing structure and the plurality oflongitudinal waveguides.
 17. The multichannel optical coupler array ofclaim 1, wherein the cross sectional configuration comprises a ringsurrounding said plurality of longitudinal waveguides.
 18. Themultichannel optical coupler array of claim 17, wherein the plurality oflongitudinal waveguides are in a hexagonal arrangement.
 19. Themultichannel optical coupler array of claim 17, wherein the ring has acircular inner cross section.
 20. The multichannel optical coupler arrayof claim 17, wherein the ring has a non-circular inner cross section.21. The multichannel optical coupler array of claim 17, wherein the ringhas a circular outer cross section.
 22. The multichannel optical couplerarray of claim 17, wherein the ring has a non-circular outer crosssection.
 23. The multichannel optical coupler array of claim 1, whereinthe cross sectional configuration comprises a structure with a pluralityof holes.
 24. The multichannel optical coupler array of claim 23,wherein the holes are in a hexagonal arrangement.
 25. The multichanneloptical coupler array of claim 23, wherein the holes are in arectangular arrangement.
 26. The multichannel optical coupler array ofclaim 23, wherein said plurality of holes is defined in an XY array. 27.The multichannel optical coupler array of claim 23, wherein at least onehole has a circular cross section.
 28. The multichannel optical couplerarray of claim 23, wherein at least one hole has a non-circular crosssection.
 29. The multichannel optical coupler array of claim 23, whereinat least one of the holes has a different dimension than another one ofthe holes.
 30. The multichannel optical coupler array of claim 23,wherein at least one of the holes has a different shape than another oneof the holes.